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.

#include<iostream>#include<string.h>using namespace std;string longestPalindrome(string s) {    int len = s.size();    int newlen = len * 2 + 1;    char str[newlen];    int p[newlen];    int i, j, k, r, id;    int maxr = 0;    str[0] = '#';    for(i = 1, j = 0 ;s[j] != '\0'; i++, j++) {        str[i] = s[j];        str[++i] = '#';    }        str[i] = '\0';    p[0] = 1;    for(i = 1, r = 1, id = 0; i < newlen; i++) {        if(r > i) p[i] = (p[id * 2 - i] < (r - i))?p[id * 2 - i]:(r - i);        else p[i] = 1;        while(str[i + p[i]] != '\0' && str[i + p[i]] == str[i - p[i]])  p[i]++;          if(p[i] >= maxr) {            maxr = p[i];            id = i;            r = i + p[i] - 1;        }    }    string str1 = s.substr((id - maxr + 1) / 2, maxr - 1);    return str1;}int main() {    string str1 = longestPalindrome("c");    cout << str1 << endl;}