OpenJudge 2971 抓住那头牛

 1 #include<iostream>
 2 #include<algorithm>
 3 #include<cstdio>
 4 #include<cmath>
 5 using namespace std;
 6 int n,k;
 7 bool vis[300001];
 8 int pos[1000000];
 9 int step[1000000];
10 void BFS(){
11     int hd=0,tl=1;
12     pos[++hd]=n;
13     step[hd]=0;
14     while(hd<=tl){
15         int now=pos[hd];
16         if(now==k){
17             printf("%d\n",step[hd]);
18             return;
19         }
20         int next=now*2;
21         if(next>=0 && next<=100000 && !vis[next]){
22             vis[next]=1;
23             pos[++tl]=next;
24             step[tl]=step[hd]+1;}
25         next=now+1;
26         if(next<=100000 && !vis[next]){
27             pos[++tl]=next;
28             vis[next]=1;
29             step[tl]=step[hd]+1;}
30         next=now-1;
31         if(next>=0 && !vis[next] ){
32             vis[next]=1;
33             pos[++tl]=next;
34             step[tl]=step[hd]+1;}
35         hd++;
36     }
37 }
38 int main(){
39     scanf("%d%d",&n,&k);
40     BFS();
41     return 0;
42 }