--hdu2717->搜索的範圍控制

C - 開

Time Limit:2000MS     Memory Limit:32768KB     64bit IO Format:%I64d & %I64u

Submit Status Practice HDU 2717

Description

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?

 

Input

Line 1: Two space-separated integers: N and K

 

Output

Line 1: The least amount of time, in minutes, it takes for Farmer John to catch the fugitive cow.

 

Sample Input

5 17

 

Sample Output

4

Hint

The fastest way for Farmer John to reach the fugitive cow is to move along the following path: 5-10-9-18-17, which takes 4 minutes. 

之所以把這個水題貼上，是爲了警戒自己，數組超限與範圍判斷的時候，應該先進行範圍判斷，然後進行數組操作！

#include<stdio.h>
#include<string.h>
#include<queue>
#include<algorithm>
using namespace std;
int vis[300010];

int bfs(int x,int ans){

    queue<int>q;
    queue<int>num;
    q.push(x);
    num.push(0);
    while(!q.empty()){

        int xx = q.front();
        int nn = num.front();
        num.pop();
        q.pop();

        if(xx == ans)return nn;
        if(xx>=0&&vis[xx-1] == 0){
            q.push(xx-1);
            num.push(nn+1);
            vis[xx-1] = 1;
        }
        if(xx+1<=ans&&vis[xx+1] == 0){
            q.push(xx+1);
            num.push(nn+1);
            vis[xx+1] = 1;
        }

        if(2*xx <=ans*2&&vis[2*xx] == 0){
            q.push(2*xx);
            num.push(nn+1);
            vis[2*xx] = 1;
        }

    }

}

int main(){


    int n,m;

    while(~scanf("%d%d",&n,&m)){
         memset(vis,0,sizeof(vis));
         vis[n]=1;
         printf("%d\n",bfs(n,m));

    }
}