python/TangDou/LuoGuBook/20_1_9_1.cpp

#include <bits/stdc++.h>

using namespace std;

//计算数字n中有多少个二进制1
int hammingWeight(int n) {
    if (n == 0) return 0;
    int cnt = 0;
    while (n) {
        n &= (n - 1);
        cnt++;
    }
    return cnt;
}

int main() {
    int n = 10, m = 4;
    //暴力算
    int cnt = 0;
    for (int i = 0; i < (1 << n); i++)
        if (hammingWeight(i) == m) cnt++;
    cout << cnt << endl;
    return 0;
}