409. Longest Palindrome

Problem Statement

Easy

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters.

Letters are case sensitive, for example, "Aa" is not considered a palindrome.

Example 1:

Input: s = "abccccdd"
Output: 7
Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7.

Example 2:

Input: s = "a"
Output: 1
Explanation: The longest palindrome that can be built is "a", whose length is 1.

Constraints:

1 <= s.length <= 2000
s consists of lowercase and/or uppercase English letters only.

Java

Source file

class Solution {
    public int longestPalindrome(String s) {
        boolean[] freq = new boolean[58];
        int len = 0;
        char[] S = s.toCharArray();
        for (char c : S){
            if(freq[c-'A'])
                len += 2;
            freq[c-'A'] = !freq[c-'A'];
        }
        boolean single = false;
        for (char c : S)
            if(freq[c-'A'])
                return ++len;
        return len;
    }
}