Submission #745875

#	Time	Username	Problem	Language	Result	Execution time	Memory
745875		vjudge1	Event Hopping (BOI22_events)	C++14	10 / 100	1587 ms	31404 KiB

events

#include <bits/stdc++.h>

using namespace std;
using ll = long long;


int main(){

    int n, q;
    cin >> n >> q;
    vector<pair<int, int> > inter(n);


    for (int i = 0; i < n; i++){
        cin >> inter[i].first >> inter[i].second;
    }

    if (n > 1000){
        set<pair<pair<int, int>, int> > s;
        for (int i = 0; i < n; i++){
            s.insert(make_pair(inter[i], i));
        }
        
        vector<ll> tav(n, -1); 
        for (ll i = 0; i < n; i++){
            if (tav[i] != -1) continue;
            queue<ll> q;
            q.push(i);
            tav[i] = i*10000000;
            while(!q.empty()){
                ll pos = q.front();
                q.pop();
                if (s.lower_bound(make_pair(make_pair(inter[pos].second, inter[pos].second), -1)) == s.end()) continue;
                ll nextPos = s.lower_bound(make_pair(make_pair(inter[pos].second, inter[pos].second), -1)) -> second;
                if (pos != n - 1 && inter[pos].second <= inter[nextPos].second && inter[pos].second >= inter[nextPos].second){
                    tav[nextPos] = tav[pos] + 1;
                    q.push(nextPos);
                }
            }
        }
        for (int i = 0; i < q; i++){
            int a, b;
            cin >> a >> b;
            a--, b--;
            if (tav[b] - tav[a] < 0 || tav[b] - tav[a] > 999999){
                cout << "impossible" << endl;
            }
            else cout << tav[b] - tav[a] << endl;
        }
    }


    vector<vector<int> > graph(n);

    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            if (i == j) continue;
            if (inter[i].second <= inter[j].second && inter[i].second >= inter[j].first){
                graph[i].push_back(j);
            }
        }
    }


    // for (int i = 0; i < n; i++){
    //     for (int x : graph[i]) cout << x << " ";
    //     cout << endl;
    // }

    for (int i = 0; i < q; i++){
        int s, e;
        cin >> s >> e;
        s--, e--;

        queue<int> q;
        q.push(s);
        vector<int> tav(n, -1); 
        tav [s] = 0;
        while(!q.empty()){
            int pos = q.front();
            q.pop();
            for (int x : graph[pos]){
                if (tav[x] == -1){
                    tav[x] = tav[pos] + 1;
                    q.push(x);
                }
            }
        }
        if (tav[e] == -1) {
            cout << "impossible" << endl;
        }
        else cout << tav[e] << endl;
    }


    return 0;
}

/*

5 2
1 3
2 4
4 7
7 9
3 7
1 4
3 2

*/

• Subtask 1: 0 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 15
• Subtask 4: 0 / 15
• Subtask 5: 0 / 20
• Subtask 6: 0 / 30