leetcode 409. 最长回文串

class Solution:
    def longestPalindrome(self, s: str) -> int:
        ls = list(s)
        st = set(ls)
        ret = 0
        
        flag = False 
        for j in st: 
            i = s.count(j)
            if i % 2 == 0:
                ret += i
            else:
                if i > 2:
                    ret += i -1
                flag = True 
        if flag:
            ret += 1

        # print(ret)
        return ret