leetcode 5. 最长回文子串

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中心扩展法

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class Solution:
    def longestPalindrome(self, s: str) -> str:
        ret = ''

        for i in range(0, len(s)):
            s1 = self.get_palindrome(s, i, i)
            s2 = self.get_palindrome(s, i, i+1)
            
            if len(s1) > len(ret):
                ret = s1
            if len(s2) > len(ret):
                ret = s2

        return ret

    def get_palindrome(self, s, left_index, right_index):
        ret = ''
        
        while left_index >= 0 and right_index < len(s) and s[left_index] == s[right_index]:
            ret = s[left_index: right_index + 1]
            left_index -= 1
            right_index += 1

        return ret