HackerEarth Caesar’s Cipher problem solution

In this HackerEarth Caesar’s Cipher problem solution Caesar’s Cipher is a very famous encryption technique used in cryptography. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a shift of 3, D would be replaced by G, E would become H, X would become A and so on.

Encryption of a letter X by a shift K can be described mathematically as EK(X) = (X + K) % 26.

Given a plaintext and it’s corresponding ciphertext, output the minimum non-negative value of shift that was used to encrypt the plaintext or else output -1 if it is not possible to obtain the given ciphertext from the given plaintext using Caesar’s Cipher technique.

#include<bits/stdc++.h>
using namespace std;
#define N 400010
typedef long long ll;
#define INF ll(1e18)
//Template ends here
int main()
{
  int q;
  cin >> q;
  while(q--)
  {
    string s, t;
    cin >> s >> t;
    int ans = -1;
    bool flag = false;
    for(int i = 0; i < (int)s.size(); i ++)
    {
      int diff = (t[i] - s[i] + 26) % 26;
      if(ans == -1)
        ans = diff;
      if(diff == ans)
        continue;
      else
      {
        flag = true;
        break;
      }
    }
    if(flag)
      printf("-1n");
    else
      printf("%dn", ans);
  }
  return 0;
}