409. Longest Palindrome

https://leetcode.com/problems/longest-palindrome/description/
解题思路：

1. 把字符转化为相应的数字
   class Solution {
   public int longestPalindrome(String s) {
   if(s == null) return 0;
   int[] nums = new int[58];
   int res = 0;
   int flag = 0;
   for(int i = 0; i < s.length(); i++){
   nums[s.charAt(i) - 'A']++;
   }
   for(int i = 0; i < nums.length; i++){
   res += nums[i] / 2 * 2;
   if(flag == 0 && nums[i] % 2 != 0){
   res += 1;
   flag = 1;
   }
   }
   return res;
   }
   }