# [BZOJ1646][Usaco2007 Open]Catch That Cow 抓住那只牛

## 1646: [Usaco2007 Open]Catch That Cow 抓住那只牛

Time Limit: 5 Sec  Memory Limit: 64 MB Submit: 1271  Solved: 601 [Submit][Status][Discuss]

## 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?

农夫约翰被通知，他的一只奶牛逃逸了！所以他决定，马上幽发，尽快把那只奶牛抓回来．
他们都站在数轴上．约翰在N(O≤N≤100000)处，奶牛在K(O≤K≤100000)处．约翰有

那么，约翰需要多少时间抓住那只牛呢？

## Input

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

仅有两个整数N和K.

## Output

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

最短的时间．

## Sample Input

5 17
Farmer John starts at point 5 and the fugitive cow is at point 17.

## Sample Output

4

OUTPUT DETAILS:

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.

bfs
#include <queue>
#include <cstdio>
using namespace std;
int n, k, f[2000000 + 10];
queue<int> q;
bool inq[2000000 + 10] = {false};
void bfs(){
f[n] = 0;
q.push(n);
inq[n] = true;
int u, v;
while(!q.empty()){
u = q.front(); q.pop();
if(u == k) return;
if(u > k){
v = u - 1;
if(!inq[v]){
inq[v] = true;
f[v] = f[u] + 1;
q.push(v);
}
}
else{
v = u - 1;
if(v > 0 && !inq[v]){
inq[v] = true;
f[v] = f[u] + 1;
q.push(v);
}
v = u + 1;
if(!inq[v]){
inq[v] = true;
f[v] = f[u] + 1;
q.push(v);
}
v = u * 2;
if(!inq[v]){
inq[v] = true;
f[v] = f[u] + 1;
q.push(v);
}
}
}
}
int main(){
scanf("%d %d", &n, &k);
bfs();
printf("%d\n", f[k]);
return 0;
}

posted @ 2017-09-07 18:59  Elder_Giang  阅读(98)  评论(0编辑  收藏  举报