POJ 1321

dfs 简单题

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
int vis[9][9];
int mat[9][9],n,k,ans;

void dfs(int x,int y,int t)
{
    //if(k-t > n - y + 1 + (n-x+1)*n) return;
    if(t == k){
       // cout<<"test:"<<t<<" "<<x<<" "<<y<<endl;
        ans++;
        return;
    }
    if(y>n){
        dfs(x+1,1,t);
        return;
    }
    if(x>n) return;
    if(!vis[x][y] && mat[x][y]){
        //cout<<"in : "<<vis[x][y]<<" "<<x<<" "<<y<<endl;
        for(int i=1;i<=n;i++)
            vis[x][i]++ , vis[i][y]++;
        dfs(x,y+1,t+1);
        for(int i=1;i<=n;i++)
            vis[x][i]-- , vis[i][y]--;
    }
    dfs(x,y+1,t);
}

int main()
{
    freopen("test.in","rb",stdin);
    char a;
    while(scanf("%d%d",&n,&k)!=EOF){
        if(n == -1 && k==-1)
            break;
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++){
                cin>>a;
                if(a == '#') mat[i][j] = 1;
                else mat[i][j] = 0;
            }

        memset(vis,0,sizeof(vis));
        ans = 0;
        dfs(1,1,0);
        printf("%d
",ans);
    }
    return 0;
}