Leetcode-5Longest Palindromic Substring

一、问题描述

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example:

Input: "babad"Output: "bab"Note: "aba" is also a valid answer.

Example:

Input: "cbbd"Output: "bb"

二、思路分析

分别以每个字母为中心，向两边展开，寻找最长的回文字符串，

有两种情况:1、该字符正好为中心；

   2、该字符和右边的字符相同，构成中心。

三、代码

class Solution {public:    string longestPalindrome(string s) {    int n = s.length();    if (n == 0) {    return "";    }    string longest = s.substr(0,1);    for (int i = 0; i < n-1; i++) {    string temp = findstr(s, i, i); //字符是s[i]为中心    if (longest.length() < temp.length()) {    longest = temp;    }    temp = findstr(s, i, i+1);  //字符s[i]和s[i+1]为中心    if (longest.length() < temp.length()) {    longest = temp;    }    }    return longest;    }private:string findstr(string s, int l, int r) { //寻找以字符s[l]为中心的最长回文串int n = s.length();while (l >= 0&& r <= n-1&&s[l] == s[r]) {l--;r++;}return s.substr(l+1, r-l-1);}};