pku 1321 棋盘问题 DFS

http://poj.org/problem?id=1321

自己真是本了开始写了歌对于棋子有顺序的搜索，导致求出来是ans的阶乘种数了，因为k < n且不能在同一行同一列，只要按行搜索，记录列是否被访问过即可！

View Code

#include <iostream>

#include <cstdio>

#include <cstring>

#define maxn 12

using namespace std;



char map[maxn][maxn];

bool vt[maxn];

int n,m,ans;





void dfs(int x,int len)

{

    int i,j;

    if (len == m)

    {

        ans++;

        return ;

    }

    for (i = x; i < n; ++i)

    {

        for (j = 0; j < n; ++j)

        {

            if (!vt[j] && map[i][j] == '#')

            {

                vt[j] = true;

                dfs(i + 1,len + 1);

                vt[j] = false;

            }

        }

    }

}



int main()

{

    //freopen("in.txt","r",stdin);

    int i;

    while (scanf("%d%d",&n,&m))

    {

        if (n == -1 && m == -1) break;

        for (i = 0; i < n; ++i) scanf("%s",map[i]);

        memset(vt,false,sizeof(vt));

        ans = 0;

        dfs(0,0);

        printf("%d\n",ans);

    }

    return 0;

}