Largest number less than X having at most K set bits in C++

In this tutorial, we are going to write a program that finds the largest number which is less than given x and should have at most k set bits.

Let's see the steps to solve the problem.

• Initialise the numbers x and k.
• Find the set bits in the number x.
• Write a loop that iterates set bits count of x - k.
  • Update the value of x with x & (x - 1).
• Return x.

Example

Let's see the code.

 Live Demo

#include <bits/stdc++.h>
using namespace std;
int largestNumberWithKBits(int x, int k) {
   int set_bit_count = __builtin_popcount(x);
   if (set_bit_count <= k) {
      return x;
   }
   int diff = set_bit_count - k;
   for (int i = 0; i < diff; i++) {
      x &= (x - 1);
   }
   return x;
}
int main() {
   int x = 65, k = 2;
   cout << largestNumberWithKBits(x, k) << endl;
   return 0;
}

Output

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

65

Conclusion

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

Hafeezul Kareem

Published on 09-Apr-2021 13:33:31

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