Strings

Strings

Longest Palindrome

class Solution(object):
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: int
        """


        pairs = set()
        counter = 0
        for c in s:
            if c not in pairs:
                pairs.add(c)
            elif c in pairs:
                pairs.remove(c)
                counter += 2
        if pairs:
            counter += 1

        # a string that can't be a palindrome will just return 0
        return counter

• Key insight: When working with palindromes, look for a way to track pairs, and one odd character. For this problem, we leverage the notion that valid palindrome has pairs of characters, and at most one non-pair. We use a set to find pairs and if we have one, add two to our counter. At the end, if we have any more characters in our set, just add 1 to our counter. I wasn't sure how leetcode wanted to handle a string that couldn't make a palindrome, but I guess returning 0 makes sense in this context.