poj 3278 bfs

Catch That Cow

Time Limit: 2000MS		Memory Limit: 65536K
Total Submissions: 41703		Accepted: 13005

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.

Source

USACO 2007 Open Silver

 

练习怎用队列

import java.awt.Point;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

class Bfs{
	private static final int SIZE=200000;
	private int s, t;
	private boolean[] vis;
	private Queue<Point> q;
	public Bfs(int s, int t){
		this.s=s; this.t=t;
		q = new LinkedList<Point>();
		vis = new boolean[SIZE];
		for(int i=0; i<SIZE; i++) vis[i]=false;
	}
	
	public int run(){
		q.add(new Point(s,0));
		while(!q.isEmpty()){
			Point cur = q.poll();
			if(cur.x == t) return cur.y;
			int y = cur.y+1;
			if(cur.x>0 && !vis[cur.x-1]){
				q.add(new Point(cur.x-1,y));
				vis[cur.x-1]=true;
			}
			if((cur.x<<1)<SIZE && !vis[cur.x<<1]){
				q.add(new Point(cur.x<<1,y));
				vis[cur.x<<1]=true;
			}
			if(cur.x+1<SIZE && !vis[cur.x+1]){
				q.add(new Point(cur.x+1, y));
				vis[cur.x+1]=true;
			}
		}
		return SIZE>>1;
	}
}

public class Main {
	static final int INF = 200000;
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner s = new Scanner(System.in);
		while(s.hasNext()){
			int n = s.nextInt(), k=s.nextInt();
			Bfs bfs = new Bfs(n,k);
			System.out.println(bfs.run());
		}
	}
}