Catch That Cow（bfs）

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

AC代码：

        

#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;
const int N = 200010;
int s,g;
int visited[N];
struct Step
{
	int x;//位置
	int step;//步数 
	
};

queue<Step> Q;

void bfs()
{
	int X, STEP;
    while(!Q.empty())
    {
        Step tmp = Q.front();
        Q.pop();
		X = tmp.x;
		STEP = tmp.step;
        if(X == g)
        {
            printf("%d\n",STEP);
            return ;
        }
        if(X>0 && !visited[X - 1]) //要保证减1后有意义,所以要X > 0
        {
            Step temp;
            visited[X-1] = 1;
            temp.x = X - 1;
            temp.step = STEP + 1;
            Q.push(temp);
        }
        if(X<=g && !visited[X + 1])
        {
            Step temp;
            visited[X + 1] = 1;
            temp.x = X + 1;
            temp.step = STEP + 1;
            Q.push(temp);
        }
        if(X<=g && !visited[X * 2])
        {
            Step temp;
            visited[X * 2] = 1;
            temp.x = 2*X;
            temp.step = STEP + 1;
            Q.push(temp);
        }
    }
}
int main () 
{
	while(cin>>s>>g)
	{
	memset(visited,0,sizeof(visited));
	Step tem;
	tem.x=s;
	tem.step=0;
	Q.push(tem);
	visited[s]=1;
	bfs();
	}
	return 0; 
}

主要思路借鉴慕课郭炜老师。