Longest_Palindromic_Sub_String_Manecher.cpp

class Solution {
public:    
    string preProcess(string s)
    {
        int len = s.size();
        string proStr = "^";
        //string numberStr = "#";
        //string dollarStr = "$";
        
        for(int i = 0; i < len; i++)
        {
            proStr.push_back('#');
            proStr.push_back(s[i]);
        }
        proStr.push_back('#');
        proStr.push_back('$');
        
        return proStr;
        
    }
    
    string longestPalindrome(string s) {
        int len = s.size();
        if(len == 0)
            return s;
        string pS = preProcess(s);
        int len_pS = pS.size();     
        int C = 0, R = 0, i_mirror = 0;
        int arr[len_pS]; 
      
        for(int i = 0; i < len_pS; i++)
        {
            i_mirror = 2 * C - i;
            
            if(i < R)
            {
                arr[i] = min(R - i, arr[i_mirror]);
            }
            else
            {
                arr[i] = 0;
            }
            
            while(pS[i+1 + arr[i]] == pS[i - 1 - arr[i]])
            {
                arr[i]++;
            }
            
            if(i + arr[i] > R)
            {
                C = i;
                R = i + arr[i];
            } 
        }
        
        int maxLen = 0, start = 0;
        for(int i = 0; i < len_pS; i++)
        {
            if(arr[i]>maxLen){
                maxLen = arr[i];
                start = i;
            }
        }
        start = (start - maxLen)/2;
        return s.substr(start, maxLen);
    }
};