LeetCode-Hash-409. Longest Palindrome

问题：https://leetcode.com/problems/longest-palindrome/
Given a string which consists of lowercase or uppercase letters, find the length of the longest palindromes that can be built with those letters.
分析：如果字符串中元素出现次数都是偶数，那一定可以构成。如果有出现次数是奇数的，则需要减去出现次数为奇数的，但是中间可以放一个，就再加个1.a的ASCII码是96，A的ASCII码是65.
代码：