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.

LeetCode-Longest Palindromic Substring

C++:
class Solution {
public:
    string longestPalindrome(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(s.size()==0) return "";
        string ret;
        string cur;
        for(int i=0;i<s.size();i++){
            cur=findPalindrome(s,i-1,i+1);
            if(cur.size()>ret.size()) ret=cur;
            cur=findPalindrome(s,i,i+1);
            if(cur.size()>ret.size()) ret=cur;
        }
        return ret;
    }
    string findPalindrome(string s,int left,int right){
        if(left<0) return s.substr(left+1,1);
        if(right>=s.size()) return s.substr(right-1,1);
        while(left>=0&&right<s.size()){
            if(s[left]!=s[right]) break;
            left--;
            right++;
        }
        left++;
        right--;
        return s.substr(left,right-left+1);
    }
};
Java:
public class Solution {
    public String longestPalindrome(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(s==null||s.length()==0) return s;
        String ret="";
        String cur="";
        for(int i=0;i<s.length();i++){
            cur=findPalindrome(s,i-1,i+1);
            if(cur.length()>ret.length()) ret=cur;
            cur=findPalindrome(s,i,i+1);
            if(cur.length()>ret.length()) ret=cur;
        }
        return ret;
    }
    public String findPalindrome(String s,int left,int right){
        if(left<0) return s.substring(left+1,left+2);
        if(right>=s.length()) return s.substring(right-1,right);
        while(left>=0&&right<s.length()){
            if(s.charAt(left)!=s.charAt(right)) break;
            left--;
            right++;
        }
        left++;
        right--;
        return s.substring(left,right+1);
    }
}