POJ1315 Don't Get Rooked【DFS】

pure dfs

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <string>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
using namespace std;
char board[5][5];
int dir[4][2]= {0,1,0,-1,1,0,-1,0};
int vis[5][5];
int maxnum;
int n;
bool judge(int x,int y)
{
    for(int i=0; i<4; i++)
    {
        int nx=x+dir[i][0];
        int ny=y+dir[i][1];
        while(nx>=0&&nx<n&&ny>=0&&ny<n)
        {
            if(board[nx][ny]=='X') break;
            if(vis[nx][ny]) return true;
            nx+=dir[i][0];
            ny+=dir[i][1];
        }
    }
    return false;
}

void dfs(int x,int y,int num)
{
    if(num>maxnum)
        maxnum=num;
    for(int i=0; i<n; i++)
    {
        for(int j=0; j<n; j++)
        {
            if(!vis[i][j]&&!judge(i,j)&&board[i][j]&&board[i][j]=='.')
            {

                vis[i][j]=1;
                dfs(i,j,num+1);
                vis[i][j]=0;

            }
        }
    }
}
int main()
{
    while(~scanf("%d",&n)&&n)
    {
        for(int i=0; i<n; i++)
            scanf("%s",board[i]);
        maxnum=-1;
        memset(vis,0,sizeof(vis));
        dfs(0,0,0);
        cout<<maxnum<<endl;
    }



}