[LintCode] Longest Palindrome

Problem

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

This is case sensitive, for example "Aa" is not considered a palindrome here.

Notice

Assume the length of given string will not exceed 1010.

Example

Given s = "abccccdd" return 7

One longest palindrome that can be built is "dccaccd", whose length is 7.

Solution

public class Solution {
    /*
     * @param s: a string which consists of lowercase or uppercase letters
     * @return: the length of the longest palindromes that can be built
     */
    public int longestPalindrome(String s) {
        // write your code here
        int res = 0;
        //Use HashMap to store occurrence, when it's even, res adds 2 and map deletes the key
        Map<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (map.containsKey(ch)) {
                map.remove(ch);
                res += 2;
            } else {
                map.put(ch, 1);
            }
        }
        if (res < s.length()) res += 1;
        return res;
    }
}