5.最长回文子串.py

#
# @lc app=leetcode.cn id=5 lang=python3
#
# [5] 最长回文子串
#

# @lc code=start
class Solution:
    def longestPalindrome(self, s: str) -> str:
        n = len(s)
        if n < 2:
            return s
        
        max_len = 1
        begin = 0
        dp = [[False] * n for _ in range(n)]
        for i in range(n):
            dp[i][i] = True
        
        for L in range(2, n + 1):
            for i in range(n):
                j = L + i - 1
                if j >= n:
                    break
                if s[i] != s[j]:
                    dp[i][j] = False
                else:
                    if j - i < 3:
                        dp[i][j] = True
                    else:
                        dp[i][j] = dp[i + 1][j - 1]
                if dp[i][j] and j - i + 1 > max_len:
                    max_len = j - i + 1
                    begin = i
        return s[begin:begin + max_len]

# @lc code=end