poj 3278 Catch That Cow （bfs 搜索）

一直很晕，用c++16Ms过，用G++WA！！！！！！！！
http://poj.org/problem?id=3278
#include<stdio.h>
#include<string.h>
#define N 100000
int n,k,vis[N];
struct node
{
    int step;
    int num;
}p[N*10];
int  bfs()
{
    memset(vis,0,sizeof(vis));
    int head=0,tail=0;
    p[head].num=n;
    p[head].step=0;
    vis[n]=1;
    tail++;
    while(head<tail)
    {
        int l=p[head].num;
        if(l==k)return p[head].step;
          if(p[head].num+1<=N&&!vis[p[head].num+1])
          {
              p[tail].num=p[head].num+1;
              vis[p[head].num+1]=1;
              p[tail].step=p[head].step+1;
              tail++;
          }


         if(p[head].num-1>=0&&!vis[p[head].num-1])
         {
              p[tail].num=p[head].num-1;
              vis[p[head].num-1]=1;
              p[tail].step=p[head].step+1;
             tail++;
         }
         if(p[head].num*2<=N&&!vis[p[head].num*2])
         {
             p[tail].num=p[head].num*2;
             vis[p[head].num*2]=1;
         p[tail].step=p[head].step+1;
         tail++;
         }


         head++;


    }
    return 0;
}
int main()
{

    while(scanf("%d%d",&n,&k)!=EOF)
    {
       int ans= bfs();
       printf("%d\n",ans);
    }
}