不断右移位,判断个位数是否为 1,统计个数。

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int input = sc.nextInt();
            int result = numOfOne(input);
            System.out.println(result);
        }
    }

    private static int numOfOne(int input) {
        int count = 0;
        while (input > 0) {
            if ((input & 1) == 1) {
                count++;
            }
            input >>>= 1;
        }
        return count;
    }
}