抓牛(poj4001)BFS
2016-07-20 17:45
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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 KOutput
Line 1: The least amount of time, in minutes, it takes for Farmer John to catch the fugitive cow.Sample Input
5 17Sample Output
4解题思路:
建立队列,通过bfs找寻最优解
code:
#include<iostream> #include<cstdio> #include<algorithm> #include<queue> #include<cstring> using namespace std; struct node { int x,c; }pos[200000];//该点的坐标和走过的步数 int n,k; queue<node>q;//队列 bool vis[200000];//判断是否走过该点 int bfs() { int p,cnt; while(!q.empty()) { p=q.front().x; cnt=q.front().c; q.pop(); if(p==k)return cnt; if(!vis[p-1]&&p>0) { vis[p-1]=1; pos[p-1].c=cnt+1; pos[p-1].x=p-1; q.push(pos[p-1]); } if(p<k) { if(!vis[p+1]) { vis[p+1]=1; pos[p+1].c=cnt+1; pos[p+1].x=p+1; q.push(pos[p+1]); } if(!vis[2*p]) { vis[2*p]=1; pos[2*p].c=cnt+1; pos[2*p].x=2*p; q.push(pos[2*p]); } } } } int main() { cin>>n>>k; memset(vis,0,sizeof(vis)); memset(pos,0,sizeof(pos)); vis =1; pos .x=n; pos .c=0; q.push(pos ); cout<<bfs()<<endl; return 0; }
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