抓住那头牛

1.

#include <bits/stdc++.h>
#define N 100001
using namespace std;
bool vis[N];
int dir[2]={-1,1};
struct node
{
    int x;
    int step;
}q[N];
void bfs(int n,int k)
{
    int head=1,tail=1;
    vis[n]=1;
    q[tail].x=n;
    q[tail].step=0;
    tail++;
    while(head<tail)
    {
        int x=q[head].x;
        int step=q[head].step;
        if(x==k)
        {
            cout<<step;
            break;
        }
        for(int i=0;i<2;i++)
        {
            int nx=x+dir[i];
            if(1<=nx and nx<=N and vis[nx]==0)
            {
                vis[nx]=1;
                q[tail].x=nx;
                q[tail].step=step+1;
                tail++;
            }
        }
        int nx=2*x;
        if(1<=nx and nx<=N and vis[nx]==0)
        {
            vis[nx]=1;
            q[tail].x=nx;
            q[tail].step=step+1;
            tail++;
        }
        head++;
    }
}
int main()
{
    int n,k;
    cin>>n>>k;
    if(k<n)
    {
        cout<<n-k;
    } 
    else
    {
        bfs(n,k);
    }
    return 0;
}

2.

# include <bits/stdc++.h>
using namespace std;
const int maxN=1e5+1;
struct node{
    int wz,step;
    //string s;
};
queue<node>Q;
int n,k;
int vis[2*maxN];
void bfs(int start){
    Q.push({start,0});
    vis[start]=1; 
    while (!Q.empty()){
        int touwz=Q.front().wz;
        int toustep=Q.front().step;
        //string tous=Q.front().s;
        Q.pop();
        int newwz[4];//string news[4];
        newwz[1]=touwz+1;//news[1]=tous+'A';
        newwz[2]=touwz-10;//news[2]=tous+'B';
        newwz[3]=touwz*2;//news[3]=tous+'C';
        int newstep=toustep+1;    
        for (int i=1;i<=3;i++){    
            if (newwz[i]==k) {
                cout<<newstep<<endl;//cout<<news[i];
                return;
            } 
            else if(vis[newwz[i]]==0 && newwz[i]>0 && newwz[i]<=maxN-1) {
               Q.push({newwz[i],newstep       });
               vis[newwz[i]]=1;        //,news[i]
           }    
         }
    }
}
int main(){
    cin>>n>>k;
    if (n==k) cout<<0<<endl;
    else
       bfs(n); 
    return 0;
}

注：//_____加上后可以输出路径。