Find index i such that prefix of S1 and suffix of S2 till i form a palindrome when concatenated in C++

Concept

With respect of given two strings S1 and S2 of equal lengths, our task is to determine an index i such that S1[0…i] and S2[i+1…n-1] give a palindrome when concatenated together. Ithas been seen that if it is not possible to determine such an index then print -1.

Input

S1 = “pqrsu”, S2 = “wxyqp”

Output

S1[0..1] = “pq”, S2[2..n-1] = “ypq”

S1 + S2 = “pqyqp” indicates is a palindrome.

Input

S1 = “pqrst”, S2 = “qprqz”

Output

-1

Method

At first, we iterate from 0 to n (length of the string) and copy ith character from S1 to another string (assume it is S).
After that we take another temporary string temp and copy the characters of S2 from index i +1 to n.
Finally, we verify whether the string (S + temp) is palindrome or not.

Example

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
// Shows function that returns true if s is palindrome
bool isPalindrome(string str){
   int i = 0;
   int b = str.length() - 1;
   while (i< b) {
      if (str[i] != str[b])
         return false;
      i++;
      b--;
   }
   return true;
}
// Shows function to return the required index
int getIndex1(string S1, string S2, int n){
   string S = "";
   for (int i = 0; i< n; a++) {
      // Used to copy the ith character in S
      S = S + S1[i];
      string temp = "";
      // Used to copy all the character of string s2 in Temp
      for (int b = i + 1; b < n; b++)
         temp += S2[b];
      // Verify whether the string is palindrome
      if (isPalindrome(S + temp)) {
         return i;
      }
   }
   return -1;
}
// Driver code
int main(){
   string S1 = "pqrsu", S2 = "wxyqp";
   int n = S1.length();
   cout << getIndex1(S1, S2, n);
   return 0;
}