LeetCode Solutions

My solutions to LeetCode problems, organized by topic as I work through NeetCode 150. Each solution includes my approach, time/space complexity, and notes on patterns I'm learning.

Progress

Arrays & Hashing

#	Problem	Difficulty	Pattern	Solution
1	Two Sum	Easy	Brute Force	solution.py
242	Valid Anagram	Easy	Hash Map	solution.py
49	Group Anagrams	Medium	Hash Map	solution.py
217	Contains Duplicate	Easy	Hash Set	solution.py
219	Contains Duplicate II	Easy	Hash Map	solution.py
220	Contains Duplicate III	Hard	Bucketing	solution.py
347	Top K Frequent Elements	Medium	Bucket Sort	solution.py
271	Encode and Decode Strings	Medium	String Encoding	solution.py
238	Product of Array Except Self	Medium	Prefix/Suffix	solution.py
36	Valid Sudoku	Medium	Hash Set	solution.py
128	Longest Consecutive Sequence	Medium	Hash Set	solution.py

Two Pointers

#	Problem	Difficulty	Pattern	Solution
125	Valid Palindrome	Easy	Two Pointers	solution.py
167	Two Sum II	Medium	Two Pointers	solution.py
15	3Sum	Medium	Two Pointers	solution.py
11	Container With Most Water	Medium	Two Pointers	solution.py
42	Trapping Rain Water	Hard	Two Pointers	solution.py

Sliding Window

#	Problem	Difficulty	Pattern	Solution
121	Best Time to Buy and Sell Stock	Easy	Sliding Window	solution.py
3	Longest Substring Without Repeating Characters	Medium	Sliding Window	solution.py
424	Longest Repeating Character Replacement	Medium	Sliding Window	solution.py
567	Permutation in String	Medium	Fixed Window	solution.py
76	Minimum Window Substring	Hard	Variable Window	solution.py
239	Sliding Window Maximum	Hard	Monotonic Deque	solution.py

Stack

#	Problem	Difficulty	Pattern	Solution
20	Valid Parentheses	Easy	Stack	solution.py
155	Min Stack	Medium	Stack	solution.py
150	Evaluate Reverse Polish Notation	Medium	Stack	solution.py
739	Daily Temperatures	Medium	Monotonic Stack	solution.py
853	Car Fleet	Medium	Stack	solution.py
84	Largest Rectangle in Histogram	Hard	Monotonic Stack	solution.py

Binary Search

#	Problem	Difficulty	Pattern	Solution
704	Binary Search	Easy	Binary Search	solution.py
74	Search a 2D Matrix	Medium	Binary Search	solution.py
875	Koko Eating Bananas	Medium	Binary Search on Answer	solution.py
153	Find Minimum in Rotated Sorted Array	Medium	Binary Search	solution.py
33	Search in Rotated Sorted Array	Medium	Binary Search	solution.py
981	Time Based Key-Value Store	Medium	Binary Search	solution.py
4	Median of Two Sorted Arrays	Hard	Binary Search	solution.py

Linked List

#	Problem	Difficulty	Pattern	Solution
206	Reverse Linked List	Easy	Iterative pointer reversal	solution.py
21	Merge Two Sorted Lists	Easy	Dummy node, two pointers	solution.py
141	Linked List Cycle	Easy	Fast and slow pointers	solution.py
143	Reorder List	Medium	Find middle, reverse, merge	solution.py
19	Remove Nth Node From End of List	Medium	Two pointers with a fixed gap	solution.py
138	Copy List with Random Pointer	Medium	Hash map for node mapping	solution.py
2	Add Two Numbers	Medium	Simulated digit addition	solution.py
287	Find the Duplicate Number	Medium	Floyd's cycle detection on array	solution.py
146	LRU Cache	Medium	Hash map plus doubly linked list	solution.py
23	Merge k Sorted Lists	Hard	Min-heap	solution.py
25	Reverse Nodes in k-Group	Hard	Bounded iterative reversal	solution.py

Structure

Solutions are organized by topic:

• arrays-hashing/
• two-pointers/
• sliding-window/
• stack/
• binary-search/
• linked-list/
• trees/
• tries/
• heap-priority-queue/
• backtracking/
• graphs/
• dynamic-programming/
• greedy/
• intervals/
• math-geometry/

Each problem folder contains a solution.py and a README.md with notes on approach and complexity.