这个类型的题目各式各样的，好多。

409. 最长回文串

这算哪门子贪心？

  1. var longestPalindrome = function(s) {
  2.     let map = new Map();
  3.     for (let char of s) {
  4.         map.set(char, (map.get(char) || 0) + 1);
  5.     }
  7.     let totalNum = 0;
  8.     let oddNum = 0;
  9.     let hasOdd = false;
  10.     for (let [key, value] of map) {
  11.         if (value % 2) { // 奇数
  12.             oddNum += value - 1;
  13.             hasOdd = true;
  14.         } else {
  15.             totalNum += value;
  16.         }
  17.     }
  18.     hasOdd && oddNum++; // 所有的奇数和 统一 加1
  19.     totalNum += oddNum;
  21.     return totalNum;
  22. };

image.png

  1. var longestPalindrome = function(s) {
  2.     let map = new Map();
  3.     for (let char of s) {
  4.         map.set(char, (map.get(char) || 0) + 1);
  5.     }
  7.     let totalNum = 0;
  9.     for (let [key, value] of map) {
  10.         if (totalNum % 2 === 0) {
  11.             if (value % 2 === 1) {
  12.                 totalNum += value
  13.             } else {
  14.                 totalNum += Math.floor(value / 2) * 2;
  15.             }
  16.         } else {
  17.             totalNum += Math.floor(value / 2) * 2;
  18.         }
  20.     }
  22.     return totalNum;
  23. };

写法优化：

  1. var longestPalindrome = function(s) {
  2.     let map = new Map();
  3.     for (let char of s) {
  4.         map.set(char, (map.get(char) || 0) + 1);
  5.     }
  7.     let totalNum = 0;
  9.     for (let [key, value] of map) {
  10.         if ((totalNum % 2 === 0) && (value % 2 === 1)) {
  11.             totalNum += value;
  12.         } else {
  13.             totalNum += Math.floor(value / 2) * 2;
  14.         }
  15.     }
  17.     return totalNum;
  18. };

5. 最长回文子串

最长公共子串