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 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.
Source |
从一个数n到另一个数k,有三种操作,加1减1乘2,问最少几步能把n变成k
BFS水题,温暖一下。
#include <cstdio>
#include <cstring>
#include <queue>
#define MAXN 100000+5
using namespace std;
int step[MAXN];
int visited[MAXN];
queue<int> nodeQueue;
int bfs(int n,int k){
while(!nodeQueue.empty())
nodeQueue.pop();
step[n]=0;
visited[n]=1;
nodeQueue.push(n);
while(!nodeQueue.empty()){
int current=nodeQueue.front();
nodeQueue.pop();
int next;
for(int i=0;i<3;i++){
if(i==0)
next=current-1;
if(i==1)
next=current+1;
if(i==2)
next=current*2;
if(next<0||next>MAXN)
continue;
if(!visited[next]){
nodeQueue.push(next);
step[next]=step[current]+1;
visited[next]=1;
}
if(current==k)
return step[current];
}
}
}
int main() {
int n,k;
while(scanf("%d%d",&n,&k)>0){
memset(step,0, sizeof(step));
memset(visited,0, sizeof(visited));
if(n>=k)
printf("%d\n",n-k);
else
printf("%d\n",bfs(n,k));
}
return 0;
}