제출 #589422

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
589422		1zaid1	Event Hopping (BOI22_events)	C++17	100 / 100	231 ms	23332 KiB

events

#include <bits/stdc++.h>
using namespace std;
#define endl '\n'

const int M = 1e5+2;
int N = exp2(ceil(log2(M)));
struct rng {int l=INT_MAX, r, i;};
int nxt[M][30], L, R;
vector<rng> v;

rng seg[4*M];

rng comb(rng a, rng b) {
    if (a.l < b.l) return a;
    return b;
}

void update(int ind) {
    while (ind /= 2) seg[ind] = comb(seg[ind*2], seg[ind*2+1]);
}

rng query(int l = 1, int r = N, int ind = 1) {
    if (l > R || r < L) return {INT_MAX, 0, 0};
    if (L <= l && r <= R) return seg[ind];
    return comb(query(l, (l+r)/2, ind*2), query((l+r)/2+1, r, ind*2+1));
}

int lca(int p, int x) {
    int l = 20, ans = 0;
    while (v[p].l > x) {
        while (l >= 0 && v[nxt[p][l]].l < x) l--;
        if (l < 0) {
            ans++;
            break;
        }

        ans += (1<<l);
        p = nxt[p][l];
    } return ans;
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);

    int n, q;
    cin >> n >> q;

    vector<int> rs;
    vector<rng> cp; v.resize(n);
    for (auto &[l, r, i]:v) cin >> l >> r;
    for (int i = 0; i < n; i++) v[i].i = i;
    cp = v;
    sort(cp.begin(), cp.end(), [](rng a, rng b){return a.r < b.r;});
    
    for (int i = 0; i < n; i++) {
        rs.push_back(cp[i].r);

        seg[i+N] = cp[i];
        update(N+i);
    }

    for (auto [l, r, i]:v) {
        nxt[i][0] = i;
        L = lower_bound(rs.begin(), rs.end(), l)-rs.begin()+1;
        R = upper_bound(rs.begin(), rs.end(), r)-rs.begin();
        if (!R) continue;
        auto tmp = query();
        if (tmp.l < l) nxt[i][0] = tmp.i;
    }

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

    while (q--) {
        int a, b;
        cin >> a >> b; a--; b--;
        if (a == b) {
            cout << 0 << endl;
            continue;
        }

        if (v[b].r < v[a].r || v[a].r < v[nxt[b][20]].l) {
            cout << "impossible" << endl;
        } else {
            cout << lca(b, v[a].r)+1 << endl;
        }
    }

    return 0;
}
/*
8 5
1 2
3 4
1 5
6 7
5 10
10 20
15 20
999999999 1000000000
1 6
1 7
2 4
3 3
5 8

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

y = 5 \left\{1 < x < 3\right\}
y = 4 \left\{2 < x < 4\right\}
y = 3 \left\{4 < x < 7\right\}
y = 2 \left\{7 < x < 9\right\}
y = 1 \left\{3 < x < 7\right\}

*/

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