Next greater Number than N with the same quantity of digits A and B in C++

Given N, A, and B. Find the number which is greater than N with the same number of A and B digits. Let's see an example.

N = 1234
A = 2
B = 3

We need to check for every possibility of the given number of digits. There are two digits to form the number. And each digit count in the number should be the same.

Algorithm

• Initialise A, B, and N.

• Write a recursive function.

  • Check whether the current number is greater than N and has equal number of A and B digits.

  • Return the number if the above condition satisfies.

  • Add the digit A to the result.
  • Add the digit B to the result.
  • Recursively call the function with the minimum number from the above two.

Implementation

Following is the implementation of the above algorithm in C++

#include <bits/stdc++.h>
using namespace std;
long getNextGreaterElement(long result, int A, int A_Count, int B, int B_Count, int N) {
   if (result > 1e11) {
      return 1e11;
   }
   if (A_Count == B_Count && result >= N) {
      return result;
   }
   return min(getNextGreaterElement(result * 10 + A, A, A_Count + 1, B, B_Count, N),       getNextGreaterElement(result * 10 + B, A, A_Count, B, B_Count + 1, N));
}
int main() {
   int N = 1234;
   int A = 2;
   int B = 3;
   cout << getNextGreaterElement(0, A, 0, B, 0, N) << endl;
   return 0;
}

Output

If you run the above code, then you will get the following result.

2233