Submission #1026546

#	Time	Username	Problem	Language	Result	Execution time	Memory
1026546		gyg	Event Hopping (BOI22_events)	C++17	20 / 100	211 ms	31100 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;

    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];
        
        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 << "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++;

            if (j == 0) { cout << "impossible" << '\n'; continue; }
            assert(r[j] >= r[f]);
            cout << ans << '\n';
        }
    }

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