409. Longest Palindrome

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.

Note:
Assume the length of given string will not exceed 1,010.

Example:

Input:
"abccccdd"

Output:
7

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

 题目含义：给定一个字符串包含大小写，用字符串中的字符组成一个回文串求符合要求的回文串的最大长度

 

    public int longestPalindrome(String s) {
        if (s.isEmpty()) return 0;
        Map<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < s.length(); i++) {
            Character letter = s.charAt(i);
            map.put(letter, map.getOrDefault(letter, 0) + 1);
        }
        int sum = 0;
        int haveOgg = 0;
        for (Map.Entry<Character, Integer> entry : map.entrySet()) {
            int count = entry.getValue();
            if (count % 2 == 0) sum += count;
            else {
                haveOgg = 1;
                sum += count - 1;
            }
        }
        return sum + haveOgg;        
    }