Merge branch 'main' of github.com:w2xi/leetcode

Author: w2xi

README.md

@@ -134,6 +134,7 @@
 |396|[旋转函数](https://leetcode.cn/problems/rotate-function/)|[JavaScript](./algorithms/rotate-function.js)|Medium|
 |404|[左叶子之和](https://leetcode.cn/problems/sum-of-left-leaves/)|[JavaScript](./algorithms/sum-of-left-leaves.js)|Easy|
 |406|[根据身高重建队列](https://leetcode.cn/problems/queue-reconstruction-by-height/)|[JavaScript](./algorithms/queue-reconstruction-by-height.js)|Medium|
+|409|[最长回文串](https://leetcode.cn/problems/longest-palindrome/)|[JavaScript](./algorithms/longest-palindrome.js)|Easy|
 |412|[Fizz Buzz](https://leetcode.cn/problems/fizz-buzz/)|[JavaScript](./algorithms/fizz-buzz.js)|Easy|
 |414|[第三大的数](https://leetcode.cn/problems/third-maximum-number/)|[JavaScript](./algorithms/third-maximum-number.js)|Easy|
 |442|[数组中重复的数据](https://leetcode.cn/problems/find-all-duplicates-in-an-array/)|[JavaScript](./algorithms/find-all-duplicates-in-an-array.js)|Medium|

algorithms/longest-palindrome.js

@@ -0,0 +1,35 @@
+/**
+ * 409. 最长回文串
+ * @param {string} s
+ * @return {number}
+ */
+var longestPalindrome = function (s) {
+  let count = 0;
+  const map = Array(52).fill(0);
+
+  for (let i = 0; i < s.length; i++) {
+    // lower letter: 0 ~ 25
+    // upper letter: 26 ~ 51
+    let index;
+    if (s[i] < "a") {
+      // upper letter
+      index = s[i].charCodeAt() - 65 + 26;
+    } else {
+      index = s[i].charCodeAt() - 97;
+    }
+    if (map[index]) {
+      // 成双成对
+      count += 2;
+      map[index]--;
+    } else {
+      map[index]++;
+    }
+  }
+  for (let i = 0; i < map.length; i++) {
+    if (map[i] === 1) {
+      count++;
+      break;
+    }
+  }
+  return count;
+};