POJ 1321

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 using namespace std;
 5 int vis[9][9];
 6 int mat[9][9],n,k,ans;
 7 
 8 void dfs(int x,int y,int t)
 9 {
10     //if(k-t > n - y + 1 + (n-x+1)*n) return;
11     if(t == k){
12        // cout<<"test:"<<t<<" "<<x<<" "<<y<<endl;
13         ans++;
14         return;
15     }
16     if(y>n){
17         dfs(x+1,1,t);
18         return;
19     }
20     if(x>n) return;
21     if(!vis[x][y] && mat[x][y]){
22         //cout<<"in : "<<vis[x][y]<<" "<<x<<" "<<y<<endl;
23         for(int i=1;i<=n;i++)
24             vis[x][i]++ , vis[i][y]++;
25         dfs(x,y+1,t+1);
26         for(int i=1;i<=n;i++)
27             vis[x][i]-- , vis[i][y]--;
28     }
29     dfs(x,y+1,t);
30 }
31 
32 int main()
33 {
34     freopen("test.in","rb",stdin);
35     char a;
36     while(scanf("%d%d",&n,&k)!=EOF){
37         if(n == -1 && k==-1)
38             break;
39         for(int i=1;i<=n;i++)
40             for(int j=1;j<=n;j++){
41                 cin>>a;
42                 if(a == ‘#‘) mat[i][j] = 1;
43                 else mat[i][j] = 0;
44             }
45 
46         memset(vis,0,sizeof(vis));
47         ans = 0;
48         dfs(1,1,0);
49         printf("%d\n",ans);
50     }
51     return 0;
52 }