(USACO) Lasers and Mirrors

#include <bits/stdc++.h>

using namespace std;
// #define int long long
#define ld long double
#define F first
#define S second
#define el '\n'
#define cout(x) for(auto v:x)cout<<v<<' ';cout<<el
#define coutp(x) for(auto v:x)cout<<v.F<<' '<<v.S<<el
#define cin(x) for(auto &v:x)cin>>v;
#define all(x)  x.begin(),x.end()
#define ll long long
#define sz(x)  (int)x.size()
#define pi pair<ll,ll>
using ull = unsigned long long;

void solve(){
ll n;
    cin>>n;

    vector<ll>dis(n+3,-1);
    vector<pi>v(n+3);
    unordered_map<ll,vector<ll>>mp[2];
    for (int i=0;i<n+2;i++)
    {
        cin>>v[i].first>>v[i].second;
        mp[0][v[i].first].push_back(i);
        mp[1][v[i].second].push_back(i);
    }
    queue<pair<ll,bool>>q;
    dis[0]=0;
    q.push({0,0});
    q.push({0,1});
    while (!q.empty())
    {

       ll  u=q.front().first;
        ll dir=q.front().second;
        ll val=dir ? v[u].second : v[u].first;
         q.pop();
        for (auto it:mp[dir][val])
        {
            if (dis[it]==-1)q.push({it,!dir}),dis[it]=dis[u]+1;
        }
    }

    if (dis[1]==-1)cout<<-1;
    else cout<<dis[1]-1;

}

int32_t main()
{

// #ifndef ONLINE_JUDGE
//      freopen("in.txt", "r", stdin);
//    // freopen("output.txt", "w", stdout);
// #endif

    freopen("lasers.in","r",stdin);
    freopen("lasers.out","w",stdout);

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int tc = 1;
    //cin >> tc;
    for (int i = 1; i <= tc; i++)solve();
    return 0;
}
/*

 */