python#最大回文子串#动态规划

定义dp[left][right]代表s[left:right]是否为回文子串

class Solution:
    def longestPalindrome(self, s: str) -> str:
        L = len(s)
        if L <2:
            return s 
        start = 0
        maxlength = 1
        sign = []
        for _ in range(L):
            sign.append([False for i in range(L)])
        for right in range(1,L):  #外层循环为right
            for left in range(0,right): #left maxlength:
                    start = left
                    maxlength = right-left+1
        return s[start:start + maxlength]

动态规划问题很巧妙， 本题难在要找到一种方法使得遍历到dp[i][j]时，判断dp[i][j]所需的条件都已满足。需注意：构造二维数组时深浅拷贝问题。