#0409 Longest Palindrome.py

class Solution:
    def longestPalindrome(self, s: str) -> int:
        """
        This function calculates the length of the longest palindrome that can be formed using the characters in the string `s`.
        
        Args:
        s (str): The input string containing characters.

        Returns:
        int: The length of the longest palindrome that can be formed.
        """

        seen = {}
        # Count the frequency of each character in the string
        for l in s:
            seen[l] = seen.get(l, 0) + 1

        odd_found = False  # Flag to check if there's any character with an odd frequency
        total = 0  # This will store the length of the longest possible palindrome

        # Calculate the length of the palindrome
        for l in seen:
            if seen[l] % 2 == 0:  # If the frequency of the character is even
                total += seen[l]  # It can be fully included in the palindrome
            else:  # If the frequency is odd
                total += seen[l] - 1  # Include the maximum even part
                odd_found = True  # Mark that we have found an odd frequency

        # If any odd frequency was found, we can add one more character in the middle of the palindrome
        if odd_found:
            total += 1
        
        return total