PLAN 1 位运算 求x的第k位数字 x >> k & 1

class Solution {
public:
    int NumberOf1(int n) {
        int res=0;
        for(int i=0;i<32;i++){
            if(n>>i&1==1) res++;
        }
        return res;
    }
};

PLAN 2 lowbit()写法 lowbit(x) = x & -x

class Solution {
public:
    int NumberOf1(int n) {
        int res=0;
        while(n){
            n-=-n&n;
            res++;
        }
        return res;
    }
};