[leetcode]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>
using namespace std;
class Solution {
public:
    string preProcess(string s) {
      int n = s.length();
      if (n == 0) return "^$";
      string ret = "^";
      for (int i = 0; i < n; i++)
        ret += "#" + s.substr(i, 1);
     
      ret += "#$";
      return ret;
    }
     
    string longestPalindrome(string s) {
      string T = preProcess(s);
      int n = T.length();
      int *P = new int[n];
      int C = 0, R = 0;
      for (int i = 1; i < n-1; i++) {
        int i_mirror = 2*C-i; // equals to i' = C - (i-C)
        
        P[i] = (R > i) ? min(R-i, P[i_mirror]) : 0;
        
        // Attempt to expand palindrome centered at i
        while (T[i + 1 + P[i]] == T[i - 1 - P[i]])
          P[i]++;
     
        // If palindrome centered at i expand past R,
        // adjust center based on expanded palindrome.
        if (i + P[i] > R) {
          C = i;
          R = i + P[i];
        }
      }
     
      // Find the maximum element in P.
      int maxLen = 0;
      int centerIndex = 0;
      for (int i = 1; i < n-1; i++) {
        if (P[i] > maxLen) {
          maxLen = P[i];
          centerIndex = i;
        }
      }
      delete[] P;
      
      return s.substr((centerIndex - 1 - maxLen)/2, maxLen);
    }
};
int main(){
	Solution s = Solution();
	string r = s.longestPalindrome("a");
	cout << r << endl;
	return 1;
}