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Starlit Sky · In memory of a night and a girl in Pahrump, NV
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<small>In memory of a night and a girl in Pahrump, NV</small>
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<h1 class="post-title">
<a href="//2017/05/15/greedy-part2/">
Greedy_Part2
</a>
</h1>
<span class="post-date">15 May 2017</span>
<h1 id="392-is-subsequence">392. Is Subsequence</h1>
<h2 id="description">Description</h2>
<p>Given a string <strong>s</strong> and a string <strong>t</strong>, check if <strong>s</strong> is subsequence of <strong>t</strong>.</p>
<p>You may assume that there is only lower case English letters in both <strong>s</strong> and <strong>t</strong>. <strong>t</strong> is potentially a very long (length ~= 500,000) string, and <strong>s</strong> is a short string (<=100).</p>
<p>A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, <code class="highlighter-rouge">"ace"</code> is a subsequence of <code class="highlighter-rouge">"abcde"</code> while <code class="highlighter-rouge">"aec"</code> is not).</p>
<h2 id="code">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">isSubsequence</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">,</span> <span class="n">String</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span>
<span class="kt">int</span> <span class="n">ps</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="kt">int</span> <span class="n">pt</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span><span class="n">s</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">></span> <span class="n">t</span><span class="o">.</span><span class="na">length</span><span class="o">())</span> <span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span><span class="n">s</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o"><</span> <span class="mi">1</span> <span class="o">||</span> <span class="n">t</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o"><</span> <span class="mi">1</span><span class="o">)</span> <span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span><span class="n">s</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">==</span> <span class="mi">1</span><span class="o">)</span> <span class="o">{</span>
<span class="k">for</span> <span class="o">(</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">t</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">;</span> <span class="n">i</span><span class="o">++</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">s</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="mi">0</span><span class="o">)</span> <span class="o">==</span> <span class="n">t</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">i</span><span class="o">)</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">while</span> <span class="o">(</span> <span class="n">ps</span> <span class="o"><</span> <span class="n">s</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">&&</span> <span class="n">pt</span> <span class="o"><</span> <span class="n">t</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">s</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">ps</span><span class="o">)</span> <span class="o">==</span> <span class="n">t</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">pt</span><span class="o">)</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">ps</span><span class="o">++;</span>
<span class="n">pt</span><span class="o">++;</span>
<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
<span class="n">pt</span><span class="o">++;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">ps</span> <span class="o">==</span> <span class="n">s</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">&&</span> <span class="n">s</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">ps</span><span class="o">-</span><span class="mi">1</span><span class="o">)</span> <span class="o">==</span> <span class="n">t</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">pt</span><span class="o">-</span><span class="mi">1</span><span class="o">)</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments">Comments</h2>
<p>I think it can be written better. So many if statements for considering the special input.</p>
<p>The key idea is to compare every s & t elements, if it is equal, then move to the next target. Or continuing, until find some element equal. If the while loop finished and we reach the tail of the string t, we can concluded it’s a subsequence.</p>
<h1 id="402-remove-k-digits">402. Remove K Digits</h1>
<h2 id="description-1">Description</h2>
<p>Given a non-negative integer <em>num</em> represented as a string, remove <em>k</em> digits from the number so that the new number is the smallest possible.</p>
<h2 id="code-1">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="n">String</span> <span class="nf">removeKdigits</span><span class="o">(</span><span class="n">String</span> <span class="n">num</span><span class="o">,</span> <span class="kt">int</span> <span class="n">k</span><span class="o">)</span> <span class="o">{</span>
<span class="n">StringBuilder</span> <span class="n">sb</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuilder</span><span class="o">(</span><span class="n">num</span><span class="o">);</span>
<span class="k">while</span> <span class="o">(</span> <span class="n">k</span> <span class="o">></span> <span class="mi">0</span> <span class="o">)</span> <span class="o">{</span>
<span class="kt">boolean</span> <span class="n">flag</span> <span class="o">=</span> <span class="kc">true</span><span class="o">;</span>
<span class="k">for</span> <span class="o">(</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">sb</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">-</span> <span class="mi">1</span><span class="o">;</span> <span class="n">i</span><span class="o">++</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">sb</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">i</span><span class="o">)</span> <span class="o">></span> <span class="n">sb</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="o">)</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">sb</span><span class="o">.</span><span class="na">deleteCharAt</span><span class="o">(</span><span class="n">i</span><span class="o">);</span>
<span class="n">k</span><span class="o">--;</span>
<span class="n">flag</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
<span class="k">break</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">flag</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">sb</span><span class="o">.</span><span class="na">deleteCharAt</span><span class="o">(</span><span class="n">sb</span><span class="o">.</span><span class="na">length</span><span class="o">()-</span><span class="mi">1</span><span class="o">);</span>
<span class="n">k</span><span class="o">--;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">while</span><span class="o">(</span> <span class="o">!</span><span class="n">sb</span><span class="o">.</span><span class="na">toString</span><span class="o">().</span><span class="na">equals</span><span class="o">(</span><span class="s">""</span><span class="o">)</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">sb</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="mi">0</span><span class="o">)</span> <span class="o">==</span> <span class="sc">'0'</span><span class="o">)</span> <span class="o">{</span>
<span class="n">sb</span><span class="o">.</span><span class="na">deleteCharAt</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span>
<span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
<span class="k">break</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">sb</span><span class="o">.</span><span class="na">toString</span><span class="o">().</span><span class="na">equals</span><span class="o">(</span><span class="s">""</span><span class="o">)</span> <span class="o">||</span> <span class="n">sb</span><span class="o">.</span><span class="na">toString</span><span class="o">().</span><span class="na">equals</span><span class="o">(</span><span class="s">"0"</span><span class="o">))</span> <span class="o">{</span>
<span class="k">return</span> <span class="s">"0"</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">sb</span><span class="o">.</span><span class="na">toString</span><span class="o">();</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments-1">Comments</h2>
<p>Remove every first peak numbers of the string.</p>
<h3 id="prove">Prove</h3>
<p>//TODO</p>
</div>
<div class="post">
<h1 class="post-title">
<a href="//2017/05/04/yaml/">
YAML
</a>
</h1>
<span class="post-date">04 May 2017</span>
<h1 id="simple-bash-implementation">Simple Bash Implementation</h1>
<h2 id="parse-function">Parse function</h2>
<div class="language-shell highlighter-rouge"><pre class="highlight"><code><span class="c">#!/bin/sh</span>
parse_yaml<span class="o">()</span> <span class="o">{</span>
<span class="nb">local </span><span class="nv">prefix</span><span class="o">=</span><span class="nv">$2</span>
<span class="nb">local </span><span class="nv">s</span><span class="o">=</span><span class="s1">'[[:space:]]*'</span> <span class="nv">w</span><span class="o">=</span><span class="s1">'[a-zA-Z0-9_]*'</span> <span class="nv">fs</span><span class="o">=</span><span class="k">$(</span><span class="nb">echo</span> @|tr @ <span class="s1">'\034'</span><span class="k">)</span>
sed -ne <span class="s2">"s|^</span><span class="se">\(</span><span class="nv">$s</span><span class="se">\)\(</span><span class="nv">$w</span><span class="se">\)</span><span class="nv">$s</span><span class="s2">:</span><span class="nv">$s</span><span class="se">\"\(</span><span class="s2">.*</span><span class="se">\)\"</span><span class="nv">$s</span><span class="se">\$</span><span class="s2">|</span><span class="se">\1</span><span class="nv">$fs</span><span class="se">\2</span><span class="nv">$fs</span><span class="se">\3</span><span class="s2">|p"</span> <span class="se">\</span>
-e <span class="s2">"s|^</span><span class="se">\(</span><span class="nv">$s</span><span class="se">\)\(</span><span class="nv">$w</span><span class="se">\)</span><span class="nv">$s</span><span class="s2">:</span><span class="nv">$s</span><span class="se">\(</span><span class="s2">.*</span><span class="se">\)</span><span class="nv">$s</span><span class="se">\$</span><span class="s2">|</span><span class="se">\1</span><span class="nv">$fs</span><span class="se">\2</span><span class="nv">$fs</span><span class="se">\3</span><span class="s2">|p"</span> <span class="nv">$1</span> |
awk -F<span class="nv">$fs</span> <span class="s1">'{
indent = length($1)/2;
vname[indent] = $2;
for (i in vname) {if (i > indent) {delete vname[i]}}
if (length($3) > 0) {
vn=""; for (i=0; i<indent; i++) {vn=(vn)(vname[i])("_")}
printf("%s%s%s=\"%s\"\n", "'</span><span class="nv">$prefix</span><span class="s1">'",vn, $2, $3);
}
}'</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="yaml-sample">Yaml Sample</h2>
<div class="language-yaml highlighter-rouge"><pre class="highlight"><code><span class="s">development</span><span class="pi">:</span>
<span class="s">adapter</span><span class="pi">:</span> <span class="s">mysql2</span>
<span class="s">encoding</span><span class="pi">:</span> <span class="s">utf8</span>
<span class="s">database</span><span class="pi">:</span> <span class="s">my_database</span>
<span class="s">username</span><span class="pi">:</span> <span class="s">root</span>
<span class="s">password</span><span class="pi">:</span>
</code></pre>
</div>
<h2 id="test-case">Test Case</h2>
<div class="language-shell highlighter-rouge"><pre class="highlight"><code><span class="c">#!/bin/sh</span>
<span class="c"># include parse_yaml function</span>
. parse_yaml.sh
<span class="c"># read yaml file</span>
<span class="nb">eval</span> <span class="k">$(</span>parse_yaml zconfig.yml <span class="s2">"config_"</span><span class="k">)</span>
<span class="c"># access yaml content</span>
<span class="nb">echo</span> <span class="nv">$config_development_database</span>
</code></pre>
</div>
<h1 id="source">Source</h1>
<div class="language-yaml highlighter-rouge"><pre class="highlight"><code><span class="s">YAML Resources</span><span class="pi">:</span>
<span class="s">YAML 1.2 (3rd Edition)</span><span class="pi">:</span> <span class="s">http://yaml.org/spec/1.2/spec.html</span>
<span class="s">YAML 1.1 (2nd Edition)</span><span class="pi">:</span> <span class="s">http://yaml.org/spec/1.1/</span>
<span class="s">YAML 1.0 (1st Edition)</span><span class="pi">:</span> <span class="s">http://yaml.org/spec/1.0/</span>
<span class="s">YAML Issues Page</span><span class="pi">:</span> <span class="s">https://github.com/yaml/yaml/issues</span>
<span class="s">YAML Mailing List</span><span class="pi">:</span> <span class="s">yaml-core@lists.sourceforge.net</span>
<span class="s">YAML IRC Channel</span><span class="pi">:</span> <span class="s2">"</span><span class="s">#yaml</span><span class="nv"> </span><span class="s">on</span><span class="nv"> </span><span class="s">irc.freenode.net"</span>
<span class="s">YAML Cookbook (Ruby)</span><span class="pi">:</span> <span class="s">http://yaml4r.sourceforge.net/cookbook/ (local)</span>
<span class="s">YAML Reference Parser</span><span class="pi">:</span> <span class="s">http://ben-kiki.org/ypaste/</span>
<span class="s">Projects</span><span class="pi">:</span>
<span class="s">C/C++ Libraries</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">libyaml</span> <span class="c1"># "C" Fast YAML 1.1</span>
<span class="pi">-</span> <span class="s">Syck</span> <span class="c1"># (dated) "C" YAML 1.0</span>
<span class="pi">-</span> <span class="s">yaml-cpp</span> <span class="c1"># C++ YAML 1.2 implementation</span>
<span class="s">Ruby</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">psych</span> <span class="c1"># libyaml wrapper (in Ruby core for 1.9.2)</span>
<span class="pi">-</span> <span class="s">RbYaml</span> <span class="c1"># YAML 1.1 (PyYAML Port)</span>
<span class="pi">-</span> <span class="s">yaml4r</span> <span class="c1"># YAML 1.0, standard library syck binding</span>
<span class="s">Python</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">PyYAML</span> <span class="c1"># YAML 1.1, pure python and libyaml binding</span>
<span class="pi">-</span> <span class="s">ruamel.yaml</span> <span class="c1"># YAML 1.2, update of PyYAML with round-tripping of comments</span>
<span class="pi">-</span> <span class="s">PySyck</span> <span class="c1"># YAML 1.0, syck binding</span>
<span class="s">Java</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">JvYaml</span> <span class="c1"># Java port of RbYaml</span>
<span class="pi">-</span> <span class="s">SnakeYAML</span> <span class="c1"># Java 5 / YAML 1.1</span>
<span class="pi">-</span> <span class="s">YamlBeans</span> <span class="c1"># To/from JavaBeans</span>
<span class="pi">-</span> <span class="s">JYaml</span> <span class="c1"># Original Java Implementation</span>
<span class="s">Perl Modules</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">YAML</span> <span class="c1"># Pure Perl YAML Module</span>
<span class="pi">-</span> <span class="s">YAML::XS</span> <span class="c1"># Binding to libyaml</span>
<span class="pi">-</span> <span class="s">YAML::Syck</span> <span class="c1"># Binding to libsyck</span>
<span class="pi">-</span> <span class="s">YAML::Tiny</span> <span class="c1"># A small YAML subset module</span>
<span class="pi">-</span> <span class="s">PlYaml</span> <span class="c1"># Perl port of PyYAML</span>
<span class="s">C#/.NET</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">YamlDotNet</span> <span class="c1"># YAML 1.1 library with serialization support</span>
<span class="pi">-</span> <span class="s">yaml-net</span> <span class="c1"># YAML 1.1 library</span>
<span class="pi">-</span> <span class="s">yatools.net</span> <span class="c1"># (in-progress) YAML 1.1 implementation</span>
<span class="s">Golang</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">Go-yaml</span> <span class="c1"># YAML support for the Go language.</span>
<span class="pi">-</span> <span class="s">Go-gypsy</span> <span class="c1"># Simplified YAML parser written in Go.</span>
<span class="s">PHP</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">php-yaml</span> <span class="c1"># libyaml bindings (YAML 1.1)</span>
<span class="pi">-</span> <span class="s">syck</span> <span class="c1"># syck bindings (YAML 1.0)</span>
<span class="pi">-</span> <span class="s">spyc</span> <span class="c1"># yaml loader/dumper (YAML 1.?)</span>
<span class="s">OCaml</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">ocaml-syck</span> <span class="c1"># YAML 1.0 via syck bindings</span>
<span class="s">Javascript</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">JS-YAML</span> <span class="c1"># Native PyYAML port to JavaScript.</span>
<span class="pi">-</span> <span class="s">JS-YAML Online# Browserified JS-YAML demo, to play with YAML in your browser.</span>
<span class="s">Actionscript</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">as3yaml</span> <span class="c1"># port of JvYAML (1.1)</span>
<span class="s">Haskell</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">YamlReference</span> <span class="c1"># Haskell 1.2 reference parser</span>
<span class="s">Dart</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">yaml</span> <span class="c1"># YAML package for Dart</span>
<span class="s">Rust</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">yaml-rust</span> <span class="c1"># YAML 1.2 implementation in pure Rust</span>
<span class="pi">-</span> <span class="s">serde-yaml</span> <span class="c1"># YAML de/serialization of structs</span>
<span class="s">Nim</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">NimYAML</span> <span class="c1"># YAML 1.2 implementation in pure Nim</span>
<span class="s">Others</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">yamlvim (src)</span> <span class="c1"># YAML dumper/emitter in pure vimscript</span>
<span class="s">Related Projects</span><span class="pi">:</span>
<span class="pi">-</span> <span class="s">Rx</span> <span class="c1"># Multi-Language Schemata Tool for JSON/YAML</span>
<span class="pi">-</span> <span class="s">Kwalify</span> <span class="c1"># Ruby Schemata Tool for JSON/YAML</span>
<span class="pi">-</span> <span class="s">yaml_vim</span> <span class="c1"># vim syntax files for YAML</span>
<span class="pi">-</span> <span class="s">yatools.net</span> <span class="c1"># Visual Studio editor for YAML</span>
<span class="pi">-</span> <span class="s">JSON</span> <span class="c1"># Official JSON Website</span>
<span class="pi">-</span> <span class="s">Pygments</span> <span class="c1"># Python language Syntax Colorizer /w YAML support</span>
</code></pre>
</div>
</div>
<div class="post">
<h1 class="post-title">
<a href="//2017/05/04/tree-part2/">
Tree_Part2
</a>
</h1>
<span class="post-date">04 May 2017</span>
<h1 id="110-balanced-binary-tree">110. Balanced Binary Tree</h1>
<h2 id="description">Description</h2>
<p>Given a binary tree, determine if it is height-balanced.</p>
<p>For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of <em>every</em> node never differ by more than 1.</p>
<h2 id="code">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="cm">/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">isBalanced</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="kt">boolean</span><span class="o">[]</span> <span class="n">res</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">boolean</span><span class="o">[</span><span class="mi">1</span><span class="o">];</span>
<span class="n">res</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">=</span> <span class="kc">true</span><span class="o">;</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="k">return</span> <span class="n">res</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">helper</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">,</span> <span class="kt">boolean</span><span class="o">[]</span> <span class="n">res</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">root</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="k">return</span> <span class="mi">0</span><span class="o">;</span>
<span class="n">left</span> <span class="o">=</span> <span class="n">isBalanced</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">);</span>
<span class="n">right</span> <span class="o">=</span> <span class="n">isBalanced</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">);</span>
<span class="n">res</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">=</span> <span class="n">res</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">&&</span> <span class="o">(</span><span class="n">Math</span><span class="o">.</span><span class="na">abs</span><span class="o">(</span><span class="n">left</span> <span class="o">-</span> <span class="n">right</span><span class="o">)</span> <span class="o"><=</span> <span class="mi">1</span><span class="o">);</span>
<span class="k">return</span> <span class="n">Math</span><span class="o">.</span><span class="na">max</span><span class="o">(</span><span class="n">left</span><span class="o">,</span> <span class="n">right</span><span class="o">)</span> <span class="o">+</span> <span class="mi">1</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h1 id="108-convert-sorted-array-to-binary-search-tree">108. Convert Sorted Array to Binary Search Tree</h1>
<h2 id="description-1">Description</h2>
<p>Given an array where elements are sorted in ascending order, convert it to a height balanced BST.</p>
<h2 id="code-1">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="n">TreeNode</span> <span class="nf">sortedArrayToBST</span><span class="o">(</span><span class="kt">int</span><span class="o">[]</span> <span class="n">nums</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">nums</span><span class="o">.</span><span class="na">length</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">)</span> <span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
<span class="n">TreeNode</span> <span class="n">root</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TreeNode</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">,</span> <span class="mi">0</span><span class="o">,</span> <span class="n">nums</span><span class="o">.</span><span class="na">length</span> <span class="o">-</span> <span class="mi">1</span><span class="o">,</span> <span class="n">nums</span><span class="o">);</span>
<span class="k">return</span> <span class="n">root</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">helper</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">,</span> <span class="kt">int</span> <span class="n">p</span><span class="o">,</span> <span class="kt">int</span> <span class="n">q</span><span class="o">,</span> <span class="kt">int</span> <span class="o">[]</span> <span class="n">nums</span><span class="o">)</span> <span class="o">{</span>
<span class="n">m</span> <span class="o">=</span> <span class="o">(</span><span class="n">p</span> <span class="o">+</span> <span class="n">q</span><span class="o">)</span> <span class="o">/</span> <span class="mi">2</span><span class="o">;</span>
<span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">=</span> <span class="n">nums</span><span class="o">[</span><span class="n">m</span><span class="o">];</span>
<span class="k">if</span> <span class="o">(</span><span class="n">p</span> <span class="o"><=</span> <span class="n">m</span> <span class="o">-</span> <span class="mi">1</span><span class="o">)</span> <span class="o">{</span>
<span class="n">root</span><span class="o">.</span><span class="na">left</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TreeNode</span><span class="o">();</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">p</span><span class="o">,</span> <span class="n">m</span> <span class="o">-</span> <span class="mi">1</span><span class="o">,</span> <span class="n">nums</span><span class="o">);</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(</span><span class="n">q</span> <span class="o">>=</span> <span class="n">m</span> <span class="o">+</span> <span class="mi">1</span><span class="o">)</span> <span class="o">{</span>
<span class="n">root</span><span class="o">.</span><span class="na">right</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TreeNode</span><span class="o">();</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">,</span> <span class="n">m</span> <span class="o">+</span> <span class="mi">1</span><span class="o">,</span> <span class="n">q</span><span class="o">,</span> <span class="n">nums</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h1 id="101-symmetric-tree">101. Symmetric Tree</h1>
<h2 id="description-2">Description</h2>
<p>Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center)</p>
<h2 id="code-2">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">isSymmetric</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">root</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">?</span> <span class="kc">true</span> <span class="o">:</span> <span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">);</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">helper</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">left</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">right</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">left</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">&&</span> <span class="n">right</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">left</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">||</span> <span class="n">right</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">left</span><span class="o">.</span><span class="na">val</span> <span class="o">==</span> <span class="n">right</span><span class="o">.</span><span class="na">val</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="nf">helper</span><span class="o">(</span><span class="n">left</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">right</span><span class="o">.</span><span class="na">right</span><span class="o">)</span> <span class="o">&&</span> <span class="n">helper</span><span class="o">(</span><span class="n">left</span><span class="o">.</span><span class="na">right</span><span class="o">,</span> <span class="n">right</span><span class="o">.</span><span class="na">left</span><span class="o">);</span>
<span class="o">}</span>
<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
</div>
<div class="post">
<h1 class="post-title">
<a href="//2017/05/03/tree-part1/">
Tree_Part1
</a>
</h1>
<span class="post-date">03 May 2017</span>
<h1 id="104-maximum-depth-of-binary-tree">104. Maximum Depth of Binary Tree</h1>
<h2 id="description">Description</h2>
<p>Given a binary tree, find its maximum depth.</p>
<p>The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.</p>
<h2 id="code">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">maxDepth</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">root</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="mi">0</span><span class="o">;</span>
<span class="k">return</span> <span class="n">Math</span><span class="o">.</span><span class="na">max</span><span class="o">(</span><span class="n">maxDepth</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">),</span> <span class="n">maxDepth</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">))</span> <span class="o">+</span> <span class="mi">1</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments">Comments</h2>
<p>Simple DFS</p>
<h1 id="226-invert-binary-tree">226. Invert Binary Tree</h1>
<h2 id="description-1">Description</h2>
<p><img src="../assets/1493854850795.png" alt="1493854850795" /></p>
<h2 id="code-1">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="cm">/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="n">TreeNode</span> <span class="nf">invertTree</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">);</span>
<span class="k">return</span> <span class="n">root</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">helper</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">root</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">swapTreeNode</span><span class="o">(</span><span class="n">root</span><span class="o">);</span>
<span class="c1">// TreeNode tmp = root.left;</span>
<span class="c1">// root.left = root.right;</span>
<span class="c1">// root.right = tmp; </span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">);</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">swapTreeNode</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="n">TreeNode</span> <span class="n">tmp</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">;</span>
<span class="n">root</span><span class="o">.</span><span class="na">left</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">;</span>
<span class="n">root</span><span class="o">.</span><span class="na">right</span> <span class="o">=</span> <span class="n">tmp</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="thinking-about-reference-in-java">Thinking about reference in Java</h2>
<h3 id="two-ways-to-swap">Two ways to swap</h3>
<h4 id="code1">code1</h4>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kt">void</span> <span class="nf">swapTreeNode</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">)</span> <span class="o">{</span>
<span class="n">TreeNode</span> <span class="n">tmp</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">;</span>
<span class="n">root</span><span class="o">.</span><span class="na">left</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">;</span>
<span class="n">root</span><span class="o">.</span><span class="na">right</span> <span class="o">=</span> <span class="n">tmp</span><span class="o">;</span>
<span class="o">}</span>
</code></pre>
</div>
<h4 id="code2">code2</h4>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="o">....</span>
<span class="n">swapTreeNode</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">)</span>
<span class="o">....</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">swapTreeNode</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">a</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">b</span><span class="o">)</span> <span class="o">{</span>
<span class="n">TreeNode</span> <span class="n">tmp</span> <span class="o">=</span> <span class="n">a</span><span class="o">;</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">b</span><span class="o">;</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">tmp</span><span class="o">;</span>
<span class="o">}</span>
</code></pre>
</div>
<p>First code is right, however, the second one makes no sense. Because of the following reasons considering java reference.</p>
<p><img src="../assets/1493856771867.png" alt="1493856771867" /></p>
<h1 id="563-binary-tree-tilt">563. Binary Tree Tilt</h1>
<h2 id="description-2">Description</h2>
<p>Given a binary tree, return the tilt of the <strong>whole tree</strong>.</p>
<p>The tilt of a <strong>tree node</strong> is defined as the <strong>absolute difference</strong> between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.</p>
<p>The tilt of the <strong>whole tree</strong> is defined as the sum of all nodes’ tilt.</p>
<h2 id="code-2">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="cm">/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">findTilt</span> <span class="o">(</span> <span class="n">TreeNode</span> <span class="n">root</span> <span class="o">)</span> <span class="o">{</span>
<span class="kt">int</span> <span class="o">[]</span> <span class="n">res</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">int</span><span class="o">[</span><span class="mi">1</span><span class="o">];</span>
<span class="n">res</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="k">return</span> <span class="n">res</span><span class="o">[</span><span class="mi">0</span><span class="o">];</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">helper</span> <span class="o">(</span> <span class="n">TreeNode</span> <span class="n">root</span><span class="o">,</span> <span class="kt">int</span> <span class="o">[]</span> <span class="n">res</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">root</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="mi">0</span><span class="o">;</span>
<span class="kt">int</span> <span class="n">left</span> <span class="o">=</span> <span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="kt">int</span> <span class="n">right</span> <span class="o">=</span> <span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="n">res</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">+=</span> <span class="n">Math</span><span class="o">.</span><span class="na">abs</span><span class="o">(</span><span class="n">left</span> <span class="o">-</span> <span class="n">right</span><span class="o">);</span>
<span class="k">return</span> <span class="n">left</span> <span class="o">+</span> <span class="n">right</span> <span class="o">+</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="think-about-one-code-cannot-work">Think about one code cannot work</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="cm">/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">findTilt</span> <span class="o">(</span> <span class="n">TreeNode</span> <span class="n">root</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">Integer</span> <span class="n">res</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Integer</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span>
<span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="k">return</span> <span class="n">res</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">helper</span> <span class="o">(</span> <span class="n">TreeNode</span> <span class="n">root</span><span class="o">,</span> <span class="n">Integer</span> <span class="n">res</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">root</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="mi">0</span><span class="o">;</span>
<span class="kt">int</span> <span class="n">left</span> <span class="o">=</span> <span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="kt">int</span> <span class="n">right</span> <span class="o">=</span> <span class="n">helper</span><span class="o">(</span><span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">,</span> <span class="n">res</span><span class="o">);</span>
<span class="n">res</span> <span class="o">+=</span> <span class="n">Math</span><span class="o">.</span><span class="na">abs</span><span class="o">(</span><span class="n">left</span> <span class="o">-</span> <span class="n">right</span><span class="o">);</span>
<span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">res</span><span class="o">);</span>
<span class="k">return</span> <span class="n">left</span> <span class="o">+</span> <span class="n">right</span> <span class="o">+</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<p>The reason it cannot work is that the value of an Integer cannot be automatic change, If you want to change the value, Java will automatic allocate a new memory, and the reference a* thus will point the memory 2, however, the a point to memory 1. This principle leads to the error.</p>
<p><img src="../assets/1493867573240.png" alt="1493867573240" /></p>
<h3 id="heres-four-solution">Here’s four solution</h3>
<ul>
<li>
<p>create a class like this</p>
<div class="highlighter-rouge"><pre class="highlight"><code>class Object {
int value;
}
</code></pre>
</div>
<p></p>
</li>
<li>
<p>use an array with one value like what I did in the code</p>
</li>
<li>
<p>don’t do that, use a return value instead</p>
</li>
<li>
<p>use a static value</p>
</li>
</ul>
<h1 id="100-same-tree">100. Same Tree</h1>
<h2 id="description-3">Description</h2>
<p>Given two binary trees, write a function to check if they are equal or not.</p>
<p>Two binary trees are considered equal if they are structurally identical and the nodes have the same value.</p>
<h2 id="code-3">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="cm">/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">isSameTree</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">p</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">q</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span><span class="o">(</span> <span class="n">p</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">&&</span> <span class="n">q</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="k">if</span><span class="o">(</span> <span class="n">p</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">||</span> <span class="n">q</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">)</span> <span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="k">return</span> <span class="n">p</span><span class="o">.</span><span class="na">val</span> <span class="o">==</span> <span class="n">q</span><span class="o">.</span><span class="na">val</span> <span class="o">?</span> <span class="n">isSameTree</span><span class="o">(</span><span class="n">p</span><span class="o">.</span><span class="na">left</span><span class="o">,</span> <span class="n">q</span><span class="o">.</span><span class="na">left</span><span class="o">)</span>
<span class="o">&&</span> <span class="n">isSameTree</span><span class="o">(</span><span class="n">p</span><span class="o">.</span><span class="na">right</span><span class="o">,</span> <span class="n">q</span><span class="o">.</span><span class="na">right</span><span class="o">)</span> <span class="o">:</span> <span class="kc">false</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments-1">Comments</h2>
<p>Beautiful Code!</p>
<h1 id="235-lowest-common-ancestor-of-a-binary-search-tree">235. Lowest Common Ancestor of a Binary Search Tree</h1>
<h2 id="description-4">Description</h2>
<p>Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.</p>
<p>According to the <a href="https://en.wikipedia.org/wiki/Lowest_common_ancestor">definition of LCA on Wikipedia</a>: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow <strong>a node to be a descendant of itself</strong>).”</p>
<h2 id="code-4">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="cm">/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/</span>
<span class="c1">//itervative</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="n">TreeNode</span> <span class="nf">lowestCommonAncestor</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">p</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">q</span><span class="o">)</span> <span class="o">{</span>
<span class="k">while</span> <span class="o">((</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">-</span> <span class="n">p</span><span class="o">.</span><span class="na">val</span> <span class="o">)</span> <span class="o">*</span> <span class="o">(</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">-</span> <span class="n">q</span><span class="o">.</span><span class="na">val</span> <span class="o">)</span> <span class="o">></span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span>
<span class="n">root</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">></span> <span class="n">p</span><span class="o">.</span><span class="na">val</span> <span class="o">?</span> <span class="n">root</span><span class="o">.</span><span class="na">left</span> <span class="o">:</span> <span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">root</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="c1">//recursive</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="n">TreeNode</span> <span class="nf">lowestCommonAncestor</span><span class="o">(</span><span class="n">TreeNode</span> <span class="n">root</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">p</span><span class="o">,</span> <span class="n">TreeNode</span> <span class="n">q</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="o">(</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">-</span> <span class="n">p</span><span class="o">.</span><span class="na">val</span> <span class="o">)</span> <span class="o">*</span> <span class="o">(</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">-</span> <span class="n">q</span><span class="o">.</span><span class="na">val</span> <span class="o">)</span> <span class="o">></span> <span class="mi">0</span> <span class="o">?</span>
<span class="n">lowestCommonAncestor</span><span class="o">(</span> <span class="n">root</span><span class="o">.</span><span class="na">val</span> <span class="o">></span> <span class="n">p</span><span class="o">.</span><span class="na">val</span> <span class="o">?</span> <span class="n">root</span><span class="o">.</span><span class="na">left</span> <span class="o">:</span> <span class="n">root</span><span class="o">.</span><span class="na">right</span><span class="o">,</span> <span class="n">p</span><span class="o">,</span> <span class="n">q</span><span class="o">):</span> <span class="n">root</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments-2">Comments</h2>
<p>For solving this question, we have the following assumption, and all the assumptions can be proved.</p>
<ol>
<li>we are going to find a node meet the formula ( root.val - p.val ) * ( root.val - q.val ) <=0</li>
<li>this node is unique</li>
<li>if we haven’t reached the node, we can prove that one of such statements must be true:
<ol>
<li>p.val < root.val && q.val < root.val</li>
<li>p.val > root.val && q.val > root.val</li>
</ol>
</li>
</ol>
</div>
<div class="post">
<h1 class="post-title">
<a href="//2017/05/03/greedy_part1/">
Greedy_Part1
</a>
</h1>
<span class="post-date">03 May 2017</span>
<p>[TOC]
NoOp</p>
<h1 id="122-best-time-to-buy-and-sell-stock-ii">122. Best Time to Buy and Sell Stock II</h1>
<h2 id="description">Description</h2>
<p>Say you have an array for which the <em>i</em>th element is the price of a given stock on day <em>i</em>.</p>
<p>Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times). However, you may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).</p>
<h2 id="code">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kt">int</span> <span class="nf">maxProfit</span><span class="o">(</span><span class="kt">int</span> <span class="o">[]</span> <span class="n">prices</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">prices</span><span class="o">.</span><span class="na">length</span> <span class="o"><</span> <span class="mi">2</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="mi">0</span><span class="o">;</span>
<span class="o">}</span>
<span class="kt">int</span> <span class="n">profit</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="k">for</span> <span class="o">(</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">prices</span><span class="o">.</span><span class="na">length</span> <span class="o">-</span> <span class="mi">1</span><span class="o">;</span><span class="n">i</span><span class="o">++</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">prices</span><span class="o">[</span><span class="n">i</span><span class="o">]</span> <span class="o"><</span> <span class="n">prices</span><span class="o">[</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="o">])</span> <span class="o">{</span>
<span class="n">profit</span> <span class="o">+=</span> <span class="n">prices</span><span class="o">[</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="o">]</span> <span class="o">-</span> <span class="n">prices</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">profit</span><span class="o">;</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments">Comments</h2>
<p>Very easy Greedy Algorithm. If the price at the <strong>step n+1</strong> is bigger than the <strong>step n</strong>, than we buy the stock at n. And vise versa, we sell the stock.</p>
<p>For the input, if the length < 2, means there are 0 or 1 price info. However, in this two situations, we can get no profit. So return 0.</p>
<h1 id="134-gas-station">134. Gas Station</h1>
<h2 id="description-1">Description</h2>
<p>There are <em>N</em> gas stations along a circular route, where the amount of gas at station <em>i</em> is <code class="highlighter-rouge">gas[i]</code>.</p>
<p>You have a car with an unlimited gas tank and it costs <code class="highlighter-rouge">cost[i]</code> of gas to travel from station <em>i</em> to its next station (<em>i</em>+1). You begin the journey with an empty tank at one of the gas stations.</p>
<p>Return the starting gas station’s index if you can travel around the circuit once, otherwise return -1.</p>
<p><strong>Note:</strong>
The solution is guaranteed to be unique.</p>
<h2 id="code-1">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">canCompleteCircuit</span><span class="o">(</span> <span class="kt">int</span> <span class="o">[]</span> <span class="n">gas</span><span class="o">,</span> <span class="kt">int</span> <span class="o">[]</span> <span class="n">cost</span> <span class="o">)</span> <span class="o">{</span>
<span class="kt">int</span> <span class="n">tank</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="kt">int</span> <span class="n">sumGas</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="kt">int</span> <span class="n">sumCost</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="kt">int</span> <span class="n">index</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="k">for</span> <span class="o">(</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">gas</span><span class="o">.</span><span class="na">length</span> <span class="o">;</span> <span class="n">i</span><span class="o">++</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">sumCost</span> <span class="o">+=</span> <span class="n">cost</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
<span class="n">sumGas</span> <span class="o">+=</span> <span class="n">gas</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
<span class="n">tank</span> <span class="o">+=</span> <span class="n">gas</span><span class="o">[</span><span class="n">i</span><span class="o">]</span> <span class="o">-</span> <span class="n">cost</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">tank</span> <span class="o"><</span> <span class="mi">0</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">index</span> <span class="o">=</span> <span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="o">;</span>
<span class="n">tank</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">sumGas</span> <span class="o"><</span> <span class="n">sumCost</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">index</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments-1">Comments</h2>
<p>It’s a good question.</p>
<p>First, think about a situation if we start at <script type="math/tex">station_p</script> and when we reach <script type="math/tex">station_q</script>, we use up the oil in our tank and thus we cannot reach the <script type="math/tex">station_{q+1}</script>.</p>
<script type="math/tex; mode=display">(1.1)\ In\ such\ situation,\ we\ assume\ that\ we\ start\ at\ every\ station\ between\ [station_p,station_q]\ cannot\ reach\ station_{q+1}.\</script>
<script type="math/tex; mode=display">(1.2) If \ \sum(oil-cost)>=0, there\ must\ be \ one \ solution</script>
<h3 id="proof-of-11">Proof of (1.1)</h3>
<p>In this case, we can introduce a <script type="math/tex">station_r</script> and <script type="math/tex">% <![CDATA[
p <= r <= q %]]></script>, from the question, we know when we reach q, we use up all the oil, so:</p>
<script type="math/tex; mode=display">% <![CDATA[
\sum_{i=p}^{q}(oil_i - cost_i) < 0 %]]></script>
<p>because p can reach r, we can get the following:</p>
<script type="math/tex; mode=display">\sum_{i=p}^{r}(oil_i - cost_i) >= 0</script>
<p>as:</p>
<script type="math/tex; mode=display">% <![CDATA[
\sum_{i=p}^{q}(oil_i - cost_i) = \sum_{i=p}^{r}(oil_i - cost_i) + \sum_{i=r}^{q}(oil_i - cost_i) < 0\\
=>
\sum_{i=r}^{q}(oil_i - cost_i) < 0 %]]></script>
<p>thus, from <script type="math/tex">station_r</script> we cannot reach <script type="math/tex">station_{q+1}</script></p>
<h3 id="implementation-of-the-algorithm">Implementation of the algorithm</h3>
<p>In the question, the answer has been guaranteed to be unique, thus, we can start from index=0, if we fail at p, it means we can discard any station between <script type="math/tex">[station_0,station_p]</script>, thus we reset the index to <script type="math/tex">p_{n+1}</script>. Continue this loop, until we reach the end of the array. If <script type="math/tex">\sum(oil-cost)>0</script>,return index, else return -1, means no solution.</p>
<h1 id="455-assign-cookies">455. Assign Cookies</h1>
<h2 id="description-2">Description</h2>
<p>Assume you are an awesome parent and want to give your children some cookies. But, you should give each child at most one cookie. Each child i has a greed factor gi, which is the minimum size of a cookie that the child will be content with; and each cookie j has a size sj. If sj >= gi, we can assign the cookie j to the child i, and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number.</p>
<p><strong>Note:</strong>
You may assume the greed factor is always positive.
You cannot assign more than one cookie to one child.</p>
<h2 id="code-2">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">findContentChildren</span><span class="o">(</span><span class="kt">int</span> <span class="o">[]</span> <span class="n">g</span><span class="o">,</span> <span class="kt">int</span><span class="o">[]</span> <span class="n">s</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span><span class="o">(</span> <span class="n">g</span><span class="o">.</span><span class="na">length</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">s</span><span class="o">.</span><span class="na">length</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">)</span> <span class="k">return</span> <span class="mi">0</span><span class="o">;</span>
<span class="n">Arrays</span><span class="o">.</span><span class="na">sort</span><span class="o">(</span><span class="n">g</span><span class="o">);</span>
<span class="n">Arrays</span><span class="o">.</span><span class="na">sort</span><span class="o">(</span><span class="n">s</span><span class="o">);</span>
<span class="kt">int</span> <span class="n">p</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
<span class="k">for</span> <span class="o">(</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">s</span><span class="o">.</span><span class="na">length</span><span class="o">;</span> <span class="n">i</span><span class="o">++</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">s</span><span class="o">[</span><span class="n">i</span><span class="o">]</span> <span class="o">>=</span> <span class="n">g</span><span class="o">[</span><span class="n">p</span><span class="o">]</span> <span class="o">)</span> <span class="o">{</span>
<span class="n">p</span><span class="o">++;</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">p</span> <span class="o">>=</span> <span class="n">g</span><span class="o">.</span><span class="na">length</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">g</span><span class="o">.</span><span class="na">length</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">p</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments-2">Comments</h2>
<p>In each step, assign the smallest cookie to the child who need a minimum size to be content with.</p>
<h1 id="55-jump-game">55. Jump Game</h1>
<h2 id="description-3">Description</h2>
<p>Given an array of non-negative integers, you are initially positioned at the first index of the array.</p>
<p>Each element in the array represents your maximum jump length at that position.</p>
<p>Determine if you are able to reach the last index.</p>
<h2 id="code-3">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">canJump</span><span class="o">(</span><span class="kt">int</span> <span class="o">[]</span> <span class="n">nums</span><span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">nums</span><span class="o">.</span><span class="na">length</span> <span class="o"><</span> <span class="mi">2</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">for</span> <span class="o">(</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">nums</span><span class="o">.</span><span class="na">length</span> <span class="o">-</span> <span class="mi">1</span><span class="o">;</span> <span class="n">i</span><span class="o">++</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">nums</span><span class="o">[</span><span class="n">i</span><span class="o">]</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">)</span> <span class="o">{</span>
<span class="kt">int</span> <span class="n">j</span> <span class="o">=</span> <span class="n">i</span> <span class="o">-</span> <span class="mi">1</span><span class="o">;</span>
<span class="k">while</span> <span class="o">(</span> <span class="n">j</span> <span class="o">>=</span> <span class="mi">0</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">nums</span><span class="o">[</span><span class="n">j</span><span class="o">]</span> <span class="o">-</span> <span class="o">(</span><span class="n">i</span> <span class="o">-</span> <span class="n">j</span><span class="o">)</span> <span class="o">></span> <span class="mi">0</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">break</span><span class="o">;</span>
<span class="o">}</span>
<span class="n">j</span><span class="o">--;</span>
<span class="o">}</span>
<span class="k">if</span> <span class="o">(</span> <span class="n">j</span> <span class="o"><</span> <span class="mi">0</span> <span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre>
</div>
<h2 id="comments-3">Comments</h2>
<p>This question can be converted to whether or not to jump over every position valued of 0. You need to consider the following things:</p>
<ol>
<li>can every 0 be jumped</li>
<li>what will happen the 0 located at the tail of nums</li>
<li>what will happen when 0 located at the start</li>
</ol>
<h1 id="253-meeting-rooms-ii">253. Meeting Rooms II</h1>
<h2 id="description-4">Description</h2>
<p>Given an array of meeting time intervals consisting of start and end times <code class="highlighter-rouge">[[s1,e1],[s2,e2],...]</code> (si < ei), find the minimum number of conference rooms required.</p>
<h2 id="code-4">Code</h2>
<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">java.util.Collections</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">java.util.Comparator</span><span class="o">;</span>
<span class="cm">/**
* Definition for an interval.
* public class Interval {
* int start;
* int end;
* Interval() { start = 0; end = 0; }
* Interval(int s, int e) { start = s; end = e; }
* }
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Solution</span> <span class="o">{</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">minMeetingRooms</span><span class="o">(</span><span class="n">Interval</span><span class="o">[]</span> <span class="n">intervals</span><span class="o">)</span> <span class="o">{</span>
<span class="n">Arrays</span><span class="o">.</span><span class="na">sort</span><span class="o">(</span><span class="n">intervals</span><span class="o">,</span> <span class="k">new</span> <span class="n">Comparator</span><span class="o"><</span><span class="n">Interval</span><span class="o">>()</span> <span class="o">{</span>
<span class="nd">@Override</span>
<span class="kd">public</span> <span class="kt">int</span> <span class="nf">compare</span><span class="o">(</span><span class="n">Interval</span> <span class="n">i1</span><span class="o">,</span> <span class="n">Interval</span> <span class="n">i2</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">i1</span><span class="o">.</span><span class="na">start</span> <span class="o">-</span> <span class="n">i2</span><span class="o">.</span><span class="na">start</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">});</span>