POJ-3278 Catch the cow(BFS)
2016-12-21 16:55
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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.
#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
const int maxx=1000010;
queue<int> bfs_q;//bfs的队列
long long n,k;
bool visit[2*maxx]; //设定访问数组记录该点是否访问过
int step[maxx];//记录访问到该点时的步数
int BFS(){
bfs_q.push(n); //首元素压入队列
step
=0;
visit
=true;
while(!bfs_q.empty()){
long long head,next;
head=bfs_q.front(); //每次从头取数 取完就pop掉...
bfs_q.pop();
for(int i=-1;i<=1;i++){ //每次有三个状态
if(i==-1) next=head-1;
else if(i==0) next=head+1;
else next=head*2;
if(next<0||next>maxx) continue; //越界处理
if(!visit[next]){ //如果该点没有被访问过
bfs_q.push(next); //把该点压入队列
visit[next]=true; //标记为已访问
step[next]=step[head]+1;
}
if(next==k){
return step[next];
}
}
}
}
int main(){
scanf("%lld %lld",&n,&k);
memset(visit,false,sizeof(bool));
memset(step,0,sizeof(int));
if(n>=k){
printf("%d\n",n-k); //如果人在牛前面...直接...
}
else{
printf("%d\n",BFS());
}
return 0;
}
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.
#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
const int maxx=1000010;
queue<int> bfs_q;//bfs的队列
long long n,k;
bool visit[2*maxx]; //设定访问数组记录该点是否访问过
int step[maxx];//记录访问到该点时的步数
int BFS(){
bfs_q.push(n); //首元素压入队列
step
=0;
visit
=true;
while(!bfs_q.empty()){
long long head,next;
head=bfs_q.front(); //每次从头取数 取完就pop掉...
bfs_q.pop();
for(int i=-1;i<=1;i++){ //每次有三个状态
if(i==-1) next=head-1;
else if(i==0) next=head+1;
else next=head*2;
if(next<0||next>maxx) continue; //越界处理
if(!visit[next]){ //如果该点没有被访问过
bfs_q.push(next); //把该点压入队列
visit[next]=true; //标记为已访问
step[next]=step[head]+1;
}
if(next==k){
return step[next];
}
}
}
}
int main(){
scanf("%lld %lld",&n,&k);
memset(visit,false,sizeof(bool));
memset(step,0,sizeof(int));
if(n>=k){
printf("%d\n",n-k); //如果人在牛前面...直接...
}
else{
printf("%d\n",BFS());
}
return 0;
}
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