思路

bfs() + 结构体queue (包含queue头文件)
queue:
1. empty()
2. size()
3. push()
4. pop()

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

const int N = 1e5 + 10;

struct pos
{
    int x, step;
};

queue<pos> q;

int n, k;
bool vis[N];

void bfs()
{
    while(!q.empty()) 
        q.pop();
    pos now, nxt;
    now.x = n;
    now.step = 0;
    q.push(now);
    while(q.size())
    {
        now = q.front();
        q.pop();
        vis[now.x] = 1;
        if(now.x == k)
        {
            cout << now.step << endl;
            return ;
        }
        for(int i = 1; i <= 3; i ++ )
        {
            if(i == 1)  
                nxt.x = now.x + 1;
            if(i == 2)
                nxt.x = now.x - 1;
            if(i == 3)
                nxt.x = now.x * 2;      
            if(nxt.x < 0 || nxt.x > N || vis[nxt.x]) 
                continue;
            vis[nxt.x] = 1;
            nxt.step = now.step + 1;
            q.push(nxt);
        }
    }
}

int main()
{
    while(cin >> n >> k)
    {
        memset(vis, 0, sizeof vis);
        if(n >= k) 
            cout << n - k << endl;
        else
            bfs();
    }
    return 0;
}