leetcode 5. 最长回文子串

leetcode [​​5. 最长回文子串​​](https://leetcode-cn.com/problems/median-of-two-sorted-arrays/)

给你一个字符串 ​​s​​​，找到 ​​s​​ 中最长的回文子串。

动态规划法求解最大回文串。

class Solution {
public:
    string longestPalindrome(string s) {
        bool dp[1005][1005];     //存储状态
        int len = s.length(),ans = 1,from = 0;
        for(int i = 0;i < len;++i)     //状态初始化
            dp[i][i] = true;
        for(int i = 0,j = len - 1;i < j;++i)
            if(s[i] == s[i + 1])
                dp[i][i + 1] = true,ans = 2,from = i;
            else
                dp[i][i + 1] = false;
        for(int i = 2,j = len;i < j;++i)    //状态方程
            for(int p = 0,q = len - i;p < q;++p)
                if(s[p] == s[p + i]){
                    if(dp[p + 1][p + i - 1])
                        dp[p][p + i] = true,ans = i + 1,from = p;
                    else
                        dp[p][p + i] = false;
                }
                else
                    dp[p][p + i] = false;
        return s.substr(from,ans);
    }
};