刷题5. Longest Palindromic Substring

一、题目说明

Longest Palindromic Substring，求字符串中的最长的回文。

Difficuty是Medium

二、我的实现

经过前面4个题目，我对边界考虑越来越“完善”了。

总共提交了5次：

第1、2次：Wrong Answer

主要是"cbbd"错误了，重复的判断逻辑上出了点小问题

第3、4次： Time Limit Exceeded

我本地代码运行没问题的，但是提交后，报错。给了一个超长的用例：

321012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210123210012321001232100123210123

我本地运行是no problem，但是提交后不行。

我继续优化代码，第5次提交终于对了。本次提交代码性能如下：

Runtime: 488 ms, faster than 5.81% of C++ online submissions for Longest Palindromic Substring.
Memory Usage: 8.7 MB, less than 91.03% of C++ online submissions for Longest Palindromic Substring.

完整代码如下

#include<iostream>
#include<string>
using namespace std;

class Solution{
	public:
		string longestPalindrome(string s){
			int maxLength=1;
			string maxStr = s.substr(0,1);
			
			int len = s.length();
			if(len<=1){
				return s;
			}else{
				int i = 0;
				while(i<len){
					int j = len-1;
					while(j>i){
						int t=i,k=j;
						while(t<k && s[t]==s[k]){
							t++;
							k--;
						}
						if(t==k || t==k+1 && s[t]==s[k]){
							if(j-i+1>maxLength){
								maxLength = j-i+1;
								maxStr = s.substr(i,j-i+1);
							}
							break;
						}
						j--;	
					}

					i++;
				}
			}
			return maxStr;
		}
};

int main(){
	Solution s;
	cout<<s.longestPalindrome("ac")<<endl;
 	cout<<s.longestPalindrome("babad")<<endl;
	cout<<s.longestPalindrome("cbbd")<<endl;	 
      cout<<s.longestPalindrome("321012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210012321001232100123210123210012321001232100123210123"); 
	
	return 0;
}