HDU 3929 Big Coefficients（容斥+证明）

(1 + x)^n 的奇数项系数个数等于 2^(bitcount(n))，bitcount(x)为x有多少个1.

然后容斥

枚举每一项存在不存在，然后容斥加加减减即可

这题用二进制枚举会T，只能DFS

代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 15;
typedef long long ll;

int t, n;
ll a[N];

int bitcount(ll x) {
    if (x == 0) return 0;
    return bitcount(x>>1) + (x&1);
}

ll pow2[100];
ll ans;

void dfs(int u, ll w, int s) {
    for (int i = u; i < n; i++) {
        ll ss = (w&a[i]);
        ans += pow2[bitcount(ss)] * s;
        dfs(i + 1, ss, s * -2);
    }
}

int main() {
    pow2[0] = 1;
    int cas = 0;
    for (int i = 1; i < 60; i++) pow2[i] = pow2[i - 1] * 2;
    scanf("%d", &t);
    while (t--) {
        scanf("%d", &n);
        ans = 0;
        for (int i = 0; i < n; i++) scanf("%I64d", &a[i]);
        dfs(0, (1LL<<50) - 1, 1);
        printf("Case #%d: %I64d\n", ++cas, ans);
    }
    return 0;
}