救命啊啊啊啊啊啊啊啊啊啊啊啊啊 30 Wrong Answer @

#include <bits/stdc++.h>
using namespace std;
const int N = 8 + 10;

int n, m;
unsigned long long ans;
bool a[N][N];
char c;

void dfs(int x, int y)
{
	if (m == 0)
	{
		ans++;
		return ;
	}
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
			if (a[i][j] and i != x and j != y)
			{
				a[i][j] = false;
				m--;
				dfs(i, j);
				a[i][j] = true;
				m++;
			}
}

int main()
{
	while(cin >> n >> m)
	{
		if (n == -1 and m == -1)
			break;
		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= n; j++)
			{
				cin >> c;
				if (c == '#')
					a[i][j] = true;
				else
					a[i][j] = false;
			}
		dfs(0, 0);
		cout << ans << endl;
		ans = 0;
	}
	
	return 0;
}