0409. Longest Palindrome

https://leetcode.com/problems/longest-palindrome

Description

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 here.

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

Example 3:

**Input:** s = "bb"
**Output:** 2

Constraints:

• 1 <= s.length <= 2000

• s consists of lowercase and/or uppercase English letters only.

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class Solution {
    public int longestPalindrome(String s) {
        Map<Character, Integer> map = new HashMap<>();
        for  (char c : s.toCharArray()) {
            map.put(c, map.getOrDefault(c, 0) + 1);
        }

        int sum = 0;
        boolean hasOdd = false;
        for (int v : map.values()) {
            if (v % 2 == 0) sum += v;
            else {
                sum += v - 1;
                hasOdd = true;
            }
        }

        return hasOdd ? sum + 1 : sum;
    }
}

/*
1) count letters, map or array; 2) sum all even value, sum all (odd value - 1); 3) if has odd value, +1
*/