# 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.