Submission #1026570

#	Time	Username	Problem	Language	Result	Execution time	Memory
1026570		gyg	Event Hopping (BOI22_events)	C++17	10 / 100	207 ms	40576 KiB

events

#pragma GCC optimize("O3", "unroll-loops")
#pragma GCC target("avx2")
#include <bits/stdc++.h>    
using namespace std;
using pii = pair<int, int>;
const int MAX_N = 1e5 + 5, INF = 1e9, MAX_Q = 1e5 + 5;

int n, q;
array<int, MAX_N> l, r;
unordered_map<int, vector<int>> at_r;

int n_ccs;
unordered_map<int, int> cc;

array<pii, 8 * MAX_N> st; // {r[i], i}
void update(int l, int r, pii x, int u = 1, int lo = 1, int hi = n_ccs) {
    if (l <= lo && hi <= r) { st[u] = max(st[u], x); return; }
    int mid = (lo + hi) / 2;
    if (l <= mid) update(l, r, x, 2 * u, lo, mid); 
    if (r > mid) update(l, r, x, 2 * u + 1, mid + 1, hi);
}
pii query(int i, int u = 1, int lo = 1, int hi = n_ccs) {
    if (lo == hi) return st[u];
    int mid = (lo + hi) / 2;
    if (i <= mid) return max(st[u], query(i, 2 * u, lo, mid));
    else return max(st[u], query(i, 2 * u + 1, mid + 1, hi));
}

array<array<int, 20>, MAX_N> anc;
void precomp() {
    set<int> coords;
    for (int i = 1; i <= n; i++) coords.insert(l[i]), coords.insert(r[i]);
    while (coords.size()) {
        n_ccs++, cc[*coords.begin()] = n_ccs;
        coords.erase(coords.begin());
    }

    for (int i = 1; i <= n; i++) update(cc[l[i]], cc[r[i]], {r[i], i});
    for (int i = 1; i <= n; i++) {
        pii x = query(cc[r[i]]);
        if (x == make_pair(r[i], i)) continue;
        anc[i][0] = x.second;
        // cout << i << ": " << x.second << endl;
    }

    for (int i = 1; i < 20; i++)
        for (int j = 1; j <= n; j++)
            anc[j][i] = anc[anc[j][i - 1]][i - 1];
}

int main() {
    // freopen("event.in", "r", stdin);
    cin.sync_with_stdio(false), cin.tie(0);

    cin >> n >> q;
    for (int i = 1; i <= n; i++) {
        cin >> l[i] >> r[i];
        at_r[r[i]].push_back(i);
    } 
    
    precomp();

    for (int i = 1; i <= q; i++) {
        int s, f; cin >> s >> f;
        if (s == f) { cout << 0 << '\n'; continue; }
        if (r[s] == r[f]) { cout << 1 << '\n'; continue;}
        if (r[s] > r[f]) { cout << "impossible" << '\n'; continue; }

        int j = s, ans = 0;
        for (int k = 19; k >= 0; k--)
            if (anc[j][k] != 0 && r[anc[j][k]] < r[f])
                j = anc[j][k], ans += (1 << k);
        assert(r[j] < r[f]);
        j = anc[j][0], ans++;
        assert(j == 0 || r[j] >= r[f]);

        if (r[j] == r[f] && j != f) ans++;
        else if (j != f) { cout << "impossible" << '\n'; continue; }
        
        cout << ans << '\n';
    }
}

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