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[][],vis[];
 int ans,n,k;
 void dfs(int row,int cnt)
 {

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