hdu_2717_Catch That Cow_bfs

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=2717

题解：一维简单BFS，详细看代码，0ms。

 #include<cstdio>
 #include<queue>
 using namespace std;
 const int maxn=;
 bool v[maxn];
 int n,k;
 struct nd{
     int x,step;
 };
 bool check(int x){
     if(x<||x>||v[x])return false;
     else return true;
 }
 int bfs(int s){
     for(int i=;i<=;i++)v[i]=false;//初始化标记
     queue<nd>Q;
     nd S;
     S.x=s,S.step=;
     v[s]=;
     Q.push(S);
     while(!Q.empty()){
         nd now=Q.front();Q.pop();
         if(now.x==k)return now.step;
         if(check(now.x+)){
             nd tmp;tmp.x=now.x+,tmp.step=now.step+;
             v[tmp.x]=;
             Q.push(tmp);
         }
         if(check(now.x-)){
             nd tmp;tmp.x=now.x-,tmp.step=now.step+;
             v[tmp.x]=;
             Q.push(tmp);
         }
         if(check(now.x*)){
             nd tmp;tmp.x=now.x*,tmp.step=now.step+;
             v[tmp.x]=;
             Q.push(tmp);
         }
     }
     return -;
 }
 int main(){
     while(~scanf("%d%d",&n,&k)){
         if(n>=k){printf("%d\n",n-k);continue;}//剪枝
         int ans=bfs(n);
         printf("%d\n",ans);
     }
     return ;
 }