codevs 3094 寻找sb4

#include<cstdio>
#include<iostream>
using namespace std;
int sum=0,n,ff=0,x[5]={0,1,0,0,-1},y[5]={0,0,1,-1,0},f[501][501],xx[501],yy[501];
int ans[501][501];
char map[501][501];

int main()
{
	int sbx,sby;
	scanf("%d",&n);
	for (int i=1;i<=n;i++)
	  for (int j=1;j<=n;j++) 
	   {
	   	 char r;  
		 f[i][j]=1;
	     cin>>r;
	     map[i][j]=r;
	     if (r==‘A‘) {
	     	xx[1]=i;
	     	yy[1]=j;
	     	f[i][j]=0;
		 }
		 if (r==‘B‘){
		 	sbx=i;
		 	sby=j;
		 }
	     if (r==‘2‘||r==‘4‘||r==‘0‘) f[i][j]=0;
       } 
  int head=0,tail=1;
  while (head!=tail)
  {
  	head++;
  	int aa=xx[head],bb=yy[head];
    for (int i=1;i<=4;i++)
    {
      int a=xx[head]+x[i],b=yy[head]+y[i];
	  if (f[a][b]&&a<=n&&a>0&&b<=n&&b>0)
	    {
	    	f[a][b]=0;
	    	xx[++tail]=a;
	    	yy[tail]=b;
	    	ans[a][b]=ans[aa][bb]+1;
	        if (a==sbx&&b==sby)
              {
	    	     ff=1;
			     break;
		      }
		}
    }
  }
  if (ff) cout<<ans[sbx][sby]*2;
    else cout<<"NoNE!";
}