add 1930

Author: clingoram

javascript/LeetCode/String/1930.js

@@ -0,0 +1,63 @@
+/**
+ * 1930. Unique Length-3 Palindromic Subsequences
+ * 
+ * 回傳屬於s迴文的子字串
+ *
+ * @param {string} s
+ * @return {number}
+ */
+var countPalindromicSubsequence = function(s) {
+    // 只能有3個字母，第一個字母和最後一個字母是一樣的，唯獨中間字母不同 = 迴文
+    // 會有一個字母出現至少2次 
+    
+    // solution 1.
+    // let ans = 0;
+    // let set = new Set(s);
+    // for(const char of set) {
+    //   let start = s.indexOf(char);
+    //   let end = s.lastIndexOf(char);
+
+    //   if(start < end){
+    //     ans += new Set(s.slice(start + 1, end)).size;
+    //   }
+    // }
+    // return ans;
+
+    // solution 2.
+    let map = new Map();
+    let ans =0;
+    for(let i = 0;i < s.length;++i) {
+      if (!map.has(s[i])) {
+        map.set(s[i], []);
+      }
+      map.get(s[i]).push(i);
+    }
+    console.log(map)
+    for(const [char,index] of map) {
+        const start = index[0];
+        const end = index[index.length - 1];
+        if (end - start <= 1) {
+          continue;
+        }
+
+        const set = new Set();
+        for (let i = start + 1; i < end; i++) {
+          set.add(s[i]);
+        }
+        ans += set.size;
+    }
+    return ans;
+};
+// let s = "aabca";
+/**
+ * 3
+ * The 3 palindromic subsequences of length 3 are:
+ * "aba" (subsequence of "aabca")
+ * "aaa" (subsequence of "aabca")
+ * "aca" (subsequence of "aabca")
+ */
+// let s = "uuuuu";
+// 1
+let s ="ckafnafqo"
+// 4
+console.log(countPalindromicSubsequence(s));