poj3278 BFS

#include <cstdio>
#include <queue>
#include <cstring>
using namespace std;
struct node
{
    int x,step;
};
const int M=200010;
int visit[M];
int bfs(int start, int aim)
{
	node v[M];
    node a,b;
    a.x=start;
    a.step=0;
    visit[start]=1;
    v[0]=a;
    int zz=1,zx=0;
    while( zz-zx>=1 )
    {
        a=v[zx];
        zx++;
        if( a.x==aim )
            return a.step;
        for(int i=0;i<3;i++)
        {
        	if(i==0 && a.x-1>=0 && a.x<=aim+1 )
        		b.x=a.x-1;
        	else if(i==1 && a.x<=aim)
        		b.x=a.x+1;
        	else if(i==2 && a.x<=aim)
        		b.x=a.x*2;
        	else
        		continue;
        	b.step=a.step+1;
        	if(  visit[b.x]==0 && b.x<=2*aim )
        	{
        		v[zz++]=b;
                visit[b.x]=1;
        	}    
        }    
    }
}

int main()
{
    // freopen("in","r",stdin);
    // freopen("out","w",stdout);
    int n,k,i;
    while(scanf("%d%d",&n,&k)!=EOF)
    {
        memset(visit,0,sizeof(visit));
        if(n>k)
        	printf("%d\n",n-k);
        else
        	printf("%d\n",bfs(n,k));
    }
    return 0;
}