棋盘问题(dfs)

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

思路：按行搜索，回溯时还原棋盘。

#include <stdio.h>
#include <string.h>
int map[9][9],vis[9];
int ans,n,k;
void dfs(int row,int cnt)
{

    if (k==cnt)
    {
        ans++;
        return ;
    }
    if (row > n)
        return ;
    for (int i = 1; i <= n; i ++)
    {
        if (map[row][i] && !vis[i])
        {
            vis[i] = 1;
            dfs(row+1,cnt+1);
            vis[i] = 0;
        }
    }
    dfs(row+1,cnt);//处理k<n的情况
    return ;
}
int main()
{
    while(~scanf("%d%d%*c",&n,&k))
    {
        if (n==-1&&k==-1)
            break;
        char ch;
        ans = 0;
        memset(map,0,sizeof(map));
        memset(vis,0,sizeof(vis));
        for (int i = 1; i <= n; i ++)
        {
            for (int j = 1; j <= n; j ++)
            {
                scanf("%c",&ch);
                if (ch=='#')
                    map[i][j] = 1;
            }
            getchar();
        }
        dfs(1,0);
        printf("%d
",ans);
    }
    return 0;
}