How many 1s are there in the binary number representation of an integer

How many 1s are there in the binary number representation of an integer

Title description

Given a 32-bit integer n, return the number of 1 in binary form of the integer.

Enter a description:

Enter an integer, representing n, where n is 32 as an integer.

Output description:

Output an integer, representing the number of 1s in the binary expression of n.

Example 1

enter

1

Output

1

Example 2

enter

-2

Output

31

Remarks:

Time complexity $O\left(1\right)$ , additional space complexity$O\left(1\right)$。

---

answer:

If enumeration is performed bitwise, 32-bit enumeration is required, which is slightly inefficient. We can only consider the bit of 1, and there are two ways to get the bit of the rightmost 1 in binary:

• n & (n - 1)
• n & (~n + 1)

Both methods can get the rightmost bit of 1 in the binary representation of n, then remove this 1 and continue processing the rest until all 1s are processed.

Code:

#include <cstdio>

using namespace std;

int main(void) {
    
    
    int n;
    scanf("%d", &n);
    int num = 0;
    while (n) {
    
    
        ++num;
        //n &= (n - 1);
        n -= n & (~n + 1);
    }
    return 0 * printf("%d\n", num);
}