2727:仙岛求药

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
const int N=21;
struct node{
    int x,y,step;
}now,nxt;
queue<node>q;
int n,m;
int a[N][N];
int xd[4]={-1,0,1,0};
int yd[4]={0,1,0,-1};
bool vis[N][N];
int sx,sy,ex,ey;
void bfs()
{
    if(sx==ex&&sy==ey)
    {
      cout<<"0"<<endl;
      return ;
    }
    while(!q.empty())q.pop();
    now.x=sx;now.y=sy;now.step=0;
    vis[sx][sy]=true;
    q.push(now);
    while(!q.empty())
     {
         now=q.front();q.pop();
         for(int i=0;i<4;i++)
          {
              int xx=now.x+xd[i];
              int yy=now.y+yd[i];
              if(xx>=1&&xx<=n&&yy>=1&&yy<=m&&!vis[xx][yy]&&a[xx][yy])
               {
                   if(xx==ex&&yy==ey)
                    {
                        cout<<now.step+1<<endl;
                        return ;
                    }
                 nxt.x=xx;
                 nxt.y=yy;
                 nxt.step=now.step+1;
                 vis[nxt.x][nxt.y]=true;
                 q.push(nxt);
               }
         } 
     }
     printf("-1
");
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {    
        if(!n) return 0;
        memset(vis,0,sizeof(vis));
        memset(a,0,sizeof(a));
     for(int i=1;i<=n;i++) 
        for(int j=1;j<=m;j++)
         {
             char ch;
             cin>>ch;
               if(ch=='#') continue;
               a[i][j]=1;
               if(ch=='@')  {  ex=i; ey=j;}
             else if(ch=='*') { sx=i; sy=j;}
         } 
     bfs();    
    } 
}