可利用宽搜解决：

#include<bits/stdc++.h>
using namespace std;
int a, b, setp[2000001];
bool v[2000001];
queue<int> q;
void push(int x, int c)
{
    if (!v[x])
    {
        q.push(x);
        v[x] = 1;
        setp[x] = c;
    }
}
int main(){
    cin >> a >> b;
    push(a, 0);
    while (!q.empty())
    {
        int x = q.front(), c = setp[x];
        q.pop();
        if (x > 0)
            push(x - 1, c + 1);
        if (x < 1000000)
            push(x + 1, c + 1);
        if (x < 1000000)
            push(x * 2, c + 1);
    }
    cout << setp[b] << endl;
	return 0;
}