Catch That Cow（poj 3278）

//广搜，a是队列，step记录步数，vis记录哪些数被搜到过
#include<cstdio>
#include<iostream>
#define M 1000010
using namespace std;
int step[M],a[M],vis[M];
int main()
{
int n,m,head=0,tail=1;
scanf("%d%d",&n,&m);
a[1]=n;
vis
=1;
while(head<tail)
{
++head;
int u=a[head];
if(u==m)
{
printf("%d",step[head]);
return 0;
}
if(u-1>=0&&!vis[u-1])
{
a[++tail]=u-1;
step[tail]=step[head]+1;
vis[u-1]=1;
}
if(u+1<1000000&&!vis[u+1])
{
a[++tail]=u+1;
step[tail]=step[head]+1;
vis[u+1]=1;
}
if(u*2<1000000&&!vis[u*2])
{
a[++tail]=u*2;
step[tail]=step[head]+1;
vis[u*2]=1;
}
}
return 0;
}