POJ 3278 Catch That Cow(BFS)
2014-01-13 19:24
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Catch That Cow
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
Sample Output
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.
题意:有一个农民和一头牛,他们在一个数轴上,牛在k位置保持不动,农户开始时在n位置。设农户当前在M位置,每次移动时有三种选择:1.移动到M-1;2.移动到M+1位置;3.移动到M*2的位置。问最少移动多少次可以移动到牛所在的位置。所以可以用广搜来搜索这三个状态,直到搜索到牛所在的位置。
Time Limit: 2000MS | Memory Limit: 65536K | |
Total Submissions: 40350 | Accepted: 12560 |
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.
题意:有一个农民和一头牛,他们在一个数轴上,牛在k位置保持不动,农户开始时在n位置。设农户当前在M位置,每次移动时有三种选择:1.移动到M-1;2.移动到M+1位置;3.移动到M*2的位置。问最少移动多少次可以移动到牛所在的位置。所以可以用广搜来搜索这三个状态,直到搜索到牛所在的位置。
#include<cstdio> #include<iostream> #include<cstring> #include<queue> #include<algorithm> using namespace std; const int N = 200100; int n, k; struct node { int x, step; }; queue<node> Q; int vis ; void BFS() { //搜索关于X的三种状态 int X, STEP; while(!Q.empty()) { node tmp = Q.front(); Q.pop(); X = tmp.x; STEP = tmp.step; if(X == k) { printf("%d\n",STEP); return ; } if(X >= 1 && !vis[X - 1]) //要保证减1后有意义,所以要X >= 1 { node temp; vis[X - 1] = 1; temp.x = X - 1; temp.step = STEP + 1; Q.push(temp); } if(X <= k && !vis[X + 1]) { node temp; vis[X + 1] = 1; temp.x = X + 1; temp.step = STEP + 1; Q.push(temp); } if(X <= k && !vis[X * 2]) { node temp; vis[X * 2] = 1; temp.x = 2 * X; temp.step = STEP + 1; Q.push(temp); } } } int main() { while(~scanf("%d%d",&n,&k)) { while(!Q.empty()) Q.pop(); memset(vis,0,sizeof(vis)); vis = 1; node t; t.x = n, t.step = 0; Q.push(t); BFS(); } return 0; }
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