记录编号	600352	评测结果	AAAAAAAAAAAAAAAAAAAA
题目名称	2001.[HZOI 2015] 厕所里的OIer	最终得分	100
用户昵称	XZDZD	是否通过	通过
代码语言	C++	运行时间	0.171 s
提交时间	2025-04-29 17:37:48	内存使用	3.66 MiB

#include<bits/stdc++.h>
#define int long long
const int N = 25;
using namespace std;
int n, m;
int f[1 << 21];
bool vis[N][N];
signed main() {
    freopen("scr_chess.in","r",stdin);
    freopen("scr_chess.out","w",stdout);
    cin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x,y;cin >> x >> y;
        vis[x - 1][y - 1] = true;
    }
    f[0] = 1;
    for (int k = 0; k < (1 << n); ++k) {
        int v = __builtin_popcount(k);
        for (int i = 0; i < n; ++i) {
            if (!(k & (1 << i))) {
               if (!vis[v][i]) {
                    f[k | (1 << i)] += f[k];
                }                 
            } 
        }
    }
    cout << f[(1 << n) - 1];
    return 0;
}