Question

I’m trying to find the number of overlapping 1 bits between 2 given numbers.

For example, given 5 and 6:

5 // 101
6 // 110

There is 1 overlapping 1 bit (the first bit)

I have following code

#include <iostream>
using namespace std;

int main() {
    int a,b;
    int count = 0;
    cin >> a >> b;
    while (a & b != 0) {
        count++;
        a >>= 1;
        b >>= 1;
    }
    cout << count << endl;

    return 0;
}

But when I entered 335 and 123 it returned 7 but I think it is not correct

Can someone see a problem with my code?

Answer 1

The problem is that you’re just printing out the number of times any of the bits match, as you lop off the least significant bit for each iteration (which will at max be the number of bits set for the smaller number). You’re comparing all bits of [a] BITWISE AND [b] each iteration. You could rectify this by masking with 1: a & b & 1, so that while you’re shift thing bits rightward each time, you’re only checking if the least significant bit is being checked:

while (a && b){
    count += a & b & 1;
    a>>=1;
    b>>=1;
}