409. Longest Palindrome | DSA Solvebook

📋Problem

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.

💡Solution

java

public class Solution {
    public int longestPalindrome(String s) {
        HashMap<Character, Integer> charFrequency = new HashMap<>();
        int oddFrequencyCount = 0;
        for (char ch : s.toCharArray()) {
            charFrequency.put(ch, charFrequency.getOrDefault(ch, 0) + 1);
            if (charFrequency.get(ch) % 2 == 1)
                oddFrequencyCount++;
            else
                oddFrequencyCount--;
        }
        if (oddFrequencyCount > 1)
            return s.length() - oddFrequencyCount + 1;
        return s.length();
    }
}

📋Problem

💡Solution

📝Editorial