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Problem 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?
* 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.
对所有状况进行一次搜索,最先找到的肯定就是时间最少的。
#include <stdio.h>#include <string.h>#include <queue>using namespace std;const int N = 1000000;int map[N+10];int n,k;struct node{ int x,step;};int check(int x){ if(x<0 || x>=N || map[x]) return 0; return 1;}int bfs(int x){ int i; queue<node> Q; node a,next; a.x = x; a.step = 0; map[x] = 1; Q.push(a); while(!Q.empty()) { a = Q.front(); Q.pop(); if(a.x == k) return a.step; next = a; //每次都将三种状况加入队列之中 next.x = a.x+1; if(check(next.x)) { next.step = a.step+1; map[next.x] = 1; Q.push(next); } next.x = a.x-1; if(check(next.x)) { next.step = a.step+1; map[next.x] = 1; Q.push(next); } next.x = a.x*2; if(check(next.x)) { next.step = a.step+1; map[next.x] = 1; Q.push(next); } } return -1;}int main(){ int ans; while(~scanf("%d%d",&n,&k)) { memset(map,0,sizeof(map)); ans = bfs(n); printf("%d\n",ans); } return 0;}