Calculate the number of 1’s in the binary representation of a number

Number of 1’s in the binary representation of a number

Complexity of the algorithm is O(Number of 1's).

bitcount(n):

count = 0

while n > 0:

            count = count + 1

            n = n & (n-1)

return count

In worst case (when the number is 2^n - 1, all 1's in binary) it will check every bit.

public class BitCount {

     public static void main(String[] args) {

           int number = 15;

           int count = 0;

           while(number>0) {

                number = number & (number-1);

                count++;

           }

           System.out.println("Number of 1s are: "+count);

     }

}

Output:

Number of 1s are: 4