wkHwNh - Online C++ Compiler & Debugging Tool

#include <bits/stdc++.h>
using namespace std;
int n, k, visited[500004], ret = -1;
queue<int> q;
int main(){
    cin >> n >> k;
    q.push(n);
    visited[n] = 1;
    int cnt = 1;
    while(q.size()){
        int here = q.front();
        q.pop();

        cout << k << ' ' << here << '\n';

        if(here == k || k > 500000){
            ret = visited[k] - 1;
            break;
        }

        k += cnt++;

        for(int next : {here + 1, here - 1, here * 2}){
            if(next < 0 || next > 500000 || visited[next]) continue;
            q.push(next);
            visited[next] = visited[here] + 1;
        }
    }

    cout << ret << '\n';
}