HDU2717 Catch That Cow 【廣搜】

標籤：hdu2717

Catch That CowTime Limit: 5000/2000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 7147    Accepted Submission(s): 2254

Problem DescriptionFarmer 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? 
InputLine 1: Two space-separated integers: N and K 
OutputLine 1: The least amount of time, in minutes, it takes for Farmer John to catch the fugitive cow. 
Sample Input

5 17

 
Sample Output

4HintThe 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. 

 

#include <stdio.h>#include <queue>#include <string.h>#define maxn 100002using std::queue;struct Node{int pos, step;};bool vis[maxn];void move(Node& tmp, int i){if(i == 0) --tmp.pos;else if(i == 1) ++tmp.pos;else tmp.pos <<= 1;}bool check(int pos){return pos >= 0 && pos < maxn && !vis[pos];}int BFS(int n, int m){if(n == m) return 0;memset(vis, 0, sizeof(vis));queue<Node> Q;Node now, tmp;now.pos = n; now.step = 0;Q.push(now);vis[n] = 1;while(!Q.empty()){now = Q.front(); Q.pop();for(int i = 0; i < 3; ++i){tmp = now;move(tmp, i);if(check(tmp.pos)){++tmp.step;if(tmp.pos == m) return tmp.step;vis[tmp.pos] = 1;Q.push(tmp);}}}}int main(){int n, m;while(scanf("%d%d", &n, &m) == 2){printf("%d\n", BFS(n, m));}return 0;}