Largest N digit number divisible by given three numbers in C++

In this tutorial, we are going to write a program that finds the largest n-digit number that is divisible by the given three numbers.

Let's see the steps to solve the problem.

• Initialise three numbers along with n.
• Find the LCM of three numbers.
• Store the largest number with n-digits.
• If the largest number is divisible by n, then return it.
• Else check for the number obtained from subtracting remainder in the above step.

Example

Let's see the code.

#include <bits/stdc++.h>
using namespace std;
int LCM(int x, int y, int z) {
   int ans = ((x * y) / (__gcd(x, y)));
   return ((z * ans) / (__gcd(ans, z)));
}
int findNumber(int n, int x, int y, int z) {
   int lcm = LCM(x, y, z);
   int largestNDigitNumber = pow(10, n) - 1;
   int remainder = largestNDigitNumber % lcm;
   if (remainder == 0) {
      return largestNDigitNumber;
   }
   largestNDigitNumber -= remainder;
   if (largestNDigitNumber >= pow(10, n - 1)) {
      return largestNDigitNumber;
   }
   return 0;
}
int main() {
   int n = 4, x = 6, y = 7, z = 8;
   int result = findNumber(n, x, y, z);
   if (result != 0) {
      cout << result << endl;
   }else {
      cout << "Not possible" << endl;
   }
   return 0;
}

Output

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

9912

Conclusion

If you have any queries in the tutorial, mention them in the comment section.