poj 3278

Farmer John has been informed of the location of a fugitive cow and wants to catch her immediately. He starts at a point N (0 ≤ N ≤ 100,000) on a number line and the cow is at a point K (0 ≤ K ≤ 100,000) on the same number line. Farmer John has two modes of transportation: walking and teleporting.

* Walking: FJ can move from any point X to the points X - 1 or X + 1 in a single minute
* Teleporting: FJ can move from any point X to the point 2 × X in a single minute.

If the cow, unaware of its pursuit, does not move at all, how long does it take for Farmer John to retrieve it?

#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
struct Node{
    int x,t;
    Node(int X,int T){
        x=X; t=T;
    }
}; 
int sign[200010];   //注意这里的标记数组要定大一些，定为100010会runtime error 
int ans;
queue <Node> q;
int main(){
    int n,k;
    while(cin>>n>>k){
        ans=9999999;
        memset(sign,0,sizeof(sign));
        while(!q.empty())
            q.pop();   //清空队列 
        int x,t;
        x=n; t=0;
        q.push(Node(x,t));        //入队 
        sign[x]=1;                //标记已访问 
        while(!q.empty()){        
            x=q.front().x; t=q.front().t;
            q.pop();
            if(x==k)
                ans=min(ans,t);
            else{
                if(x<k){
                    if(sign[x+1]==0){
                        q.push(Node(x+1,t+1));    
                        sign[x+1]=1;
                    }
                    if(sign[2*x]==0){
                        q.push(Node(2*x,t+1));
                        sign[2*x]=1;
                    }
                    if(x>0&&sign[x-1]==0){
                        q.push(Node(x-1,t+1));
                        sign[x-1]=1;
                    }
                }
                else if(x>k){
                    if(sign[x-1]==0){
                        q.push(Node(x-1,t+1));
                        sign[x-1]=1; 
                    }
                }
            }
        } 
        cout<<ans<<endl; 
    }
    return 0;
}