记录编号	101712	评测结果	AAAAAAAAAA
题目名称	棋盘放車	最终得分	100
用户昵称	FF_Sky||幻	是否通过	通过
代码语言	C	运行时间	0.359 s
提交时间	2014-05-13 21:48:07	内存使用	9.96 MiB

#include <stdio.h>

long long f[1048577];
int a[21];

inline int lowbit(int x){return x & (-x);}

int main()
{
	freopen("examone.in", "r", stdin);
	freopen("examone.out", "w", stdout);
	int n, m, x, y, c, R, i, t;
	scanf("%d%d", &n, &m);
	for (i = 0; i < m; i++)
	{
		scanf("%d%d", &x, &y);
		a[x] ^= 1<<(y-1);
	}
	R = 1<<n; f[0] = 1;
	for (i = 1; i < R; i++)
	{
		for (c = 0, t = i; t; ) c++, t -= lowbit(t);
		for (t = i&(~a[c]); t; ) f[i] += f[i^lowbit(t)], t -= lowbit(t);
	}
	printf("%lld", f[R-1]);
	return 0;
}