广搜 + 队列（queue）

#include<bits/stdc++.h>
using namespace std;
int n,k,vis[1000005];
struct node{
	int x,step;//位置，步数
};
void bfs(){
	queue<node> q; 
	q.push({n,0});
	vis[n]=1;//标记
	while(q.size()){
		node n1=q.front();
		q.pop();
		//判断队首是否到达终点
		if(n1.x==k){
//			输出步数
			cout<<n1.step;
			return;
		} 
		//用n1点去拓展新的结点  n1.x  +1 -1   n1.x*2 
		//+1
		if(n1.x+1<=100000 && n1.x+1>=0 && vis[n1.x+1]==0){
			//标记n1.x+1 ,q.push({n1.x+1,n1.step+1});
			vis[n1.x+1]=1;
			q.push({n1.x+1,n1.step+1});
		}     
		//-1
//		if(n1.x-1在界内 并且n1.x-1没走过)    标记n1.x-1 ,q.push({n1.x-1,n1.step+1}); 
		if(n1.x-1>=0 && n1.x-1<=100000 && vis[n1.x-1]==0){
			vis[n1.x-1]=1;
			q.push({n1.x-1,n1.step+1});
		}
		//*2
//		if(n1.x*2在界内 并且n1.x*2没走过)    标记n1.x*2 ,q.push({n1.x*2,n1.step+1}); 
		if(n1.x*2>=0 && n1.x*2<=100000 && vis[n1.x*2]==0){
			vis[n1.x*2]=1;
			q.push({n1.x*2,n1.step+1});
		}
	} 
}
int main(){
	//n  k
	cin>>n>>k;
	bfs();
	return 0;
}