Longest Palindrome

1import java.util.HashSet;
2
3class Solution {
4    public int longestPalindrome(String s) {
5        HashSet<Character> seenCharacters = new HashSet<Character>();
6        int count = 0;
7
8        for (int i = 0; i < s.length(); i++)
9        {
10            if (seenCharacters.contains(s.charAt(i)))
11            {
12                count += 2;
13                seenCharacters.remove(s.charAt(i));
14            }
15            else
16            {
17                seenCharacters.add(s.charAt(i));
18            }
19        }
20
21        return count < s.length() ? count + 1 : count;
22    }
23}