最长回文子串[中心扩展思想]

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

    string findLongestPalindrome(string &s)
    {
        int length=s.size();
        int maxlength=0;
        int start,j,k;  

        for(int i=0;i<length;i++)
        {
			if(length%2!=0){//奇偶判断
				j=i-1;k=i+1;
			}else{
				j=i;k=i+1;
			}
            while(j>=0&&k<length&&s.at(j)==s.at(k))
            {
                if(k-j+1>maxlength)
                {
                    maxlength=k-j+1;
                    start=j;
                }
                j--;
                k++;
            }
        }  

        if(maxlength>0)
            return s.substr(start,maxlength);
        return NULL;
    }

	void main()
	{
		string s;
		getline(cin,s);
		cout<<findLongestPalindrome(s)<<endl;
	}

更多信息：

http://blog.csdn.net/kangroger/article/details/37742639