Find nth number that contains the digit k or divisible by k in C++

Given two positive integers n and k, and we have to find the nth number that contains the digit k or divisible by k. The k will be in range [2 to 9]. So if n and k are 15 and 3 respectively, then output is 33. As the numbers [3, 6, 9, 12, 13, 15, 18, 21, 23, 24, 27, 30, 31, 33] These are those numbers where each element contains the digit k = 3 or divisibility by k and in this nth number is 33. So output is 33.

Check each number that contains k and multiple of k, and count till we get nth element.

Example

 Live Demo

#include<iostream>
using namespace std;
bool hasDigit(int n, int k) {
   while (n > 0) {
      int rem = n % 10;
      if (rem == k)
      return true;
      n = n / 10;
   }
   return false;
}
int countNumbers(int n, int k) {
   for (int i = k + 1, count = 1; count < n; i++) {
      if (hasDigit(i, k) || (i % k == 0))
         count++;
      if (count == n)
         return i;
   }
   return -1;
}
int main() {
   int n = 10, k = 2;
   cout << "Last number is " << countNumbers(n, k) << " before that the number contains " << k << " and multiple of " << k;
}

Output

Last number is 20 before that the number contains 2 and multiple of 2

Arnab Chakraborty

Published on 18-Dec-2019 16:41:34