Longest Palindromic Substring

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

思路：找出字符串s中最长的回文子串。我们可以这样考虑，从中间向两边扩展，尽可能找出最长的回文子串。在此注意要考虑奇偶位置的比较，这一点要考虑清楚。

 

class Solution {

public:

    string Sub_Palindrome(string s,int left,int right)

    {

        int l=left,r=right;

        int n=s.length();

        while(l>=0 && r<=n-1 && s[l]==s[r])

        {

            l--;

            r++;

        }

        return s.substr(l+1,r-l-1);

    }

    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 sub_str1=Sub_Palindrome(s,i,i);//奇数

            if(sub_str1.length()>longest.length())

                longest=sub_str1;

            string sub_str2=Sub_Palindrome(s,i,i+1);//偶数

            if(sub_str2.length()>longest.length())

                longest=sub_str2;

        }

        return longest;

    }

};