poj-1321 棋盘问题 DFS

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#define INF 0x3f3f3f3f

using namespace std;

int n,k,ans;
char map[20][20];
int vis[20];

void DFS(int x,int num)
{
if(num==k)
{
ans++;
return;
}
if(x>=n) return;
for (int i=0;i<n;i++)
{
if(map[x][i]=='#'&&!vis[i])
{
vis[i]=1;
DFS(x+1,num+1);
vis[i]=0;
}
}
DFS(x+1,num);
}
int main()
{
while(scanf("%d%d%*c",&n,&k),n!=-1||k!=-1)
{
ans=0;
for (int i=0;i<n;i++)
{
scanf("%s",map[i]);
}
DFS(0,0);
printf("%d\n",ans);
}
return 0;
}