最长回文子串

def solve():
    def longestPalindrome(____):
        def expand(____):
            while left >= ____ and right < len(____) and s[left] == s[right]:
                left -= ____
                right += ____
            return s[left+____:right]
        result = '____'
        for i in range(len(____)):
            s1 = expand(____)
            s2 = expand(____)
            if len(____) > len(____):
                result = s1
            if len(____) > len(____):
                result = s2
        return result
    print(longestPalindrome(____))