[409. Longest Palindrome] #leetcode

409_0913.java

class Solution {
  // O(n) O(1)
    public int longestPalindrome(String s) {
        if (s.length() == 0 || s == null) return 0;
            
        int[] counts = new int[52];
        
        for (Character c : s.toCharArray()) {
            int idx = 0;
            if (c.compareTo('a') < 0) {
                idx = (int) c - 'A';
            } else {
                idx = (int) c - 'a';
                idx += 26;
            }
            
            counts[idx]++;
        }
        
        boolean flag = false;
        int res = 0;
        for (int count :  counts) {
            if (count % 2 == 0) {
                res += count;
            } else {
                res += count - 1;
                flag = true;
            }
        }
        
        return flag? res + 1 : res;
    }
}