Submission #1211096

#	Time	Username	Problem	Language	Result	Execution time	Memory
1211096		madamadam3	Port Facility (JOI17_port_facility)	C++20	22 / 100	6091 ms	32836 KiB

port_facility

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

struct Event {
    int time, box_id;
    bool is_remove;

    const bool operator<(const Event &other) {
        return time < other.time;
    }
};

const int MAXN = 1'000'001;
const int MOD = 1'000'000'007;
int n;

int A[MAXN], B[MAXN];
vector<Event> events;

ll modexp(ll a, ll p) {
    if (p == 0) return 1;
    if (p == 1) return a;

    ll ans = modexp(a, p / 2);
    ans %= MOD;

    ans *= ans;
    ans %= MOD;

    if (p % 2 == 1) ans *= a;
    ans %= MOD;

    return ans % MOD;
}

void solve() {
    int ways = 1;
    vector<vector<int>> crossings(n, vector<int>()); // had this idea previously to precompute crossings js was trying to brute force first

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int ci = i, cj = j;
            if (A[cj] < A[ci]) swap(ci, cj);
            if (!(A[ci] < A[cj] && A[cj] < B[ci] && B[ci] < B[cj])) continue;

            crossings[ci].push_back(cj);
            crossings[cj].push_back(ci);
        }
    }
    
    vector<int> group(n, -1);
    int cmps = 0;
    
    // push the constraints down the group (ie. each incompatible thing on a different side)
    for (int i = 0; i < n; i++) {
        if (group[i] != -1) continue;
        group[i] = 1;
        cmps++;

        queue<int> q;
        q.push(i);

        while (!q.empty()) {
            int cur = q.front();
            q.pop();

            for (auto &restriction : crossings[cur]) {
                if (group[restriction] == -1) {
                    group[restriction] = group[cur] == 1 ? 2 : 1; // push down the constraint
                    q.push(restriction);
                } else if (group[restriction] == group[cur]) { // inconsistency, need to break
                    cout << 0;
                    return;
                }
            }
        }

    }

    ways = modexp(2, cmps); // either group 1 in A g2 B or g1 B g2 A so 2 ways for each cmp
    cout << ways;
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> A[i] >> B[i];
    }

    for (int i = 0; i < n; i++) {
        events.push_back(Event {A[i], i, false});
        events.push_back(Event {B[i], i, true});
    }

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

    solve();
    return 0;
}

• Subtask 1: 10 / 10
• Subtask 2: 12 / 12
• Subtask 3: 0 / 56
• Subtask 4: 0 / 22