leetcode(5)-最长回文子串

给定一个字符串 s，找到 s 中最长的回文子串。你可以假设 s 的最大长度为 1000。

题目: https://leetcode-cn.com/problems/longest-palindromic-substring/submissions/

写的不好,不容宜写剪枝。太耗时了。

class Solution:
    def longestPalindrome(self, s: str) -> str:
        index = [[0 for i in range(1005)] for j in range(1005)]
        for i in range(len(s)):
            index[i][i] = 1
        begin, end = 0, 0
        not_exist = []
        for i in range(2,len(s)+1):
            jump = False
            flag = False
            for each in not_exist:
                if (i-each)%2 == 0:
                    jump=True
                    break
            if jump:
                continue
            for j in range(0,len(s)-i+1):
                if s[j]==s[j+i-1] and (index[j+1][j+i-2]==1 or i==2):
                    index[j][j+i-1] = 1
                    begin = j
                    end = j+i-1
                    flag = True 
            if not flag:
                not_exist.append(i)
        return s[begin:end+1]