Задача №170. Автобусы OK

#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>
#include <string>
#include <stack>
#include <set>
#include <map>
#define pii pair <int,int>
#define vec vector
using namespace std;
using ll = long long;
using ld = long double;
using db = double;
void cv(vector <int> &v){
    for (auto x: v) cout<<x<<' ';
    cout<<"\n";
}

void cvl(vector <ll> &v){
    for (auto x: v) cout<<x<<' ';
    cout<<"\n";
}


void cvv(vector <vector <int> > &v){
    for (auto x: v) cv(x);
    cout<<"\n";
}

void cvb(vector <bool> v){
    for (bool x: v) cout<<x<<' ';
    cout<<"\n";
}

void cvs(vector <string>  v){
    for (auto a: v){
        cout<<a<<"\n";
    }
}

struct ed{
    int to, tout, tin;
};

const int inf = 2e9;

void sh(ed x){
    cout<<x.to<<' '<<x.tout<<' '<<x.tin<<"\n";
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n, the1st, last,r;
    cin>>n>>the1st>>last>>r;
    the1st--; last--;
    vector <vector <ed> > G(n);
    for (int i = 0; i < r; ++i){
        int fr, frt, to, tot;
        cin>>fr>>frt>>to>>tot;
        fr--; to--;
        ed e = {to, frt, tot};
        G[fr].push_back(e);
    }
    /*
    debug
    cout<<"G\n";
    for (int i = 0; i < n; ++i){
        cout<<"v = "<<i<<"\n";
        for (ed e: G[i]) sh(e);
        cout<<"\n";
    }
    cout<<"the1st last = "<<the1st<<' '<<last<<"\n";
    */

    vector <int> T(n,inf);
    T[the1st]=0;
    set <pii> Q;
    Q.insert({0, the1st});
    while (!Q.empty()){
        pii nxt = *Q.begin();
        int v = nxt.second;
        Q.erase(Q.begin());
        for (ed e: G[v]){
            int str_t = e.tout, fin_t = e.tin, u = e.to;
            if (T[u] > fin_t && str_t >= T[v]){
                Q.erase({T[u], u});
                T[u] = fin_t;
                Q.insert({T[u], u});
            }
        }
    }
    if (T[last] == inf){
        cout<<-1;
        exit(0);
    }
    cout<<T[last];
}