Submission #604458

#	Time	Username	Problem	Language	Result	Execution time	Memory
604458		Jomnoi	Event Hopping (BOI22_events)	C++17	10 / 100	1561 ms	43056 KiB

events

#include <bits/stdc++.h>
using namespace std;

const int MAX_N = 1e5 + 5;
const int MAX_M = 5005;
const int INF = 1e9 + 7;

int S[MAX_N], E[MAX_N];
int dist[MAX_N];
int can_reach[MAX_M][MAX_M];
vector <int> graph[MAX_N];
int nxt[MAX_N][20];

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    int N, Q;
    cin >> N >> Q;

    for(int i = 1; i <= N; i++) {
        cin >> S[i] >> E[i];
    }

    if(N <= 5000) {
        for(int i = 1; i <= N; i++) {
            for(int j = 1; j <= N; j++) {
                if(i != j and S[j] <= E[i] and E[i] <= E[j]) {
                    graph[i].push_back(j);
                }
            }
        }

        for(int i = 1; i <= N; i++) {
            for(int j = 1; j <= N; j++) {
                dist[j] = -1;
            }

            queue <int> q;
            q.push(i);
            dist[i] = 0;
            while(!q.empty()) {
                int u = q.front();
                q.pop();

                for(auto v : graph[u]) {
                    if(dist[v] == -1) {
                        dist[v] = dist[u] + 1;
                        q.push(v);
                    }
                }
            }

            for(int j = 1; j <= N; j++) {
                can_reach[i][j] = dist[j];
            }
        }

        while(Q--) {
            int s, e;
            cin >> s >> e;

            if(can_reach[s][e] == -1) {
                cout << "impossible\n";
            }
            else {
                cout << can_reach[s][e] << '\n';
            }
        }
    }
    else {
        vector <pair <int, int>> vec;
        for(int i = 1; i <= N; i++) {
            vec.emplace_back(E[i], S[i]);
        }

        sort(vec.begin(), vec.end());

        for(int l = 0, r = 0; l < N; r++) {
            while(r < N and vec[l].first < S[r]) {
                r++;
            }

            nxt[l][0] = r;
        }
        for(int j = 1; j < 20; j++) {
            for(int i = 0; i < N; i++) {
                nxt[i][j] = nxt[nxt[i][j - 1]][j - 1];
            }
        }

        while(Q--) {
            int s, e;
            cin >> s >> e;

            int ps = lower_bound(vec.begin(), vec.end(), make_pair(e, s)) - vec.begin();
            int pe = lower_bound(vec.begin(), vec.end(), make_pair(e, s)) - vec.begin();

            int ans = 0;
            for(int i = 19; i >= 0; i--) {
                if(nxt[ps][i] <= pe) {
                    ps = nxt[ps][i];
                    ans += (1<<i);
                }
            }
        
            if(ps == pe) {
                cout << ans << '\n';
            }
            else {
                cout << "impossible\n";
            }
        }
    }
    return 0;
}

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