Submission #722710

#	Time	Username	Problem	Language	Result	Execution time	Memory
722710		dxz05	Event Hopping (BOI22_events)	C++17	100 / 100	612 ms	27984 KiB

events

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
#define all(x) (x).begin(), (x).end()
#define MP make_pair
const int N = 100500;

template <typename T>
struct SegmentTree{
    int n = 0;
    vector<T> tree;

    T neutral_element = make_pair(1e9, -1); // e.g. 0 for sum, INF for min ...

    SegmentTree(){};
    SegmentTree(int _n){
        n = _n;
        tree.assign(n * 4 + 5, neutral_element);
    }

    inline T combine(T lf, T rg){
        return min(lf, rg); // change it
    }

    inline void build(int v, int tl, int tr, const vector<T> &a){
        if (tl == tr){
            tree[v] = a[tl];
            return;
        }
        int tm = (tl + tr) >> 1;
        build(v << 1, tl, tm, a);
        build(v << 1 | 1, tm + 1, tr, a);
        tree[v] = combine(tree[v << 1], tree[v << 1 | 1]);
    }

    inline void init(const vector<T> &a){
        n = (int)a.size();
        tree.assign(n * 4 + 5, neutral_element);
        build(1, 0, n - 1, a);
    }

    inline void update(int v, int tl, int tr, int pos, T val){
        if (tl == tr){
            tree[v] = min(tree[v], val); // pay attention!
            return;
        }
        int tm = (tl + tr) >> 1;
        if (pos <= tm){
            update(v << 1, tl, tm, pos, val);
        } else {
            update(v << 1 | 1, tm + 1, tr, pos, val);
        }
        tree[v] = combine(tree[v << 1], tree[v << 1 | 1]);
    }

    inline void update(int pos, T val){
        update(1, 0, n - 1, pos, val);
    }

    inline T get(int v, int tl, int tr, int l, int r){
        if (l <= tl && tr <= r) return tree[v];
        if (tl > r || tr < l) return neutral_element;
        int tm = (tl + tr) >> 1;
        return combine(get(v << 1, tl, tm, l, r), get(v << 1 | 1, tm + 1, tr, l, r));
    }

    inline T get(int l, int r){
        return get(1, 0, n - 1, l, r);
    }

};

int f[N][18];
int l[N], r[N];

bool can_switch(int i, int j){
    return l[j] <= r[i] && r[i] <= r[j];
}

void solve(){
    int n, q;
    cin >> n >> q;

    map<int, int> mp;
    for (int i = 0; i < n; i++){
        cin >> l[i] >> r[i];
        mp[l[i]], mp[r[i]];
    }

    int z = 0;
    for (auto &now : mp) now.second = z++;

    SegmentTree<pair<int, int>> st(n * 2);
    for (int i = 0; i < n; i++) {
        st.update(mp[r[i]], make_pair(mp[l[i]], i));
    }

    for (int i = 0; i < n; i++){
        int j = st.get(mp[l[i]], mp[r[i]]).second;
        f[i][0] = (j != -1 && l[j] < l[i] ? j : -1);
    }

    for (int j = 1; j < 18; j++){
        for (int i = 0; i < n; i++){
            int mid = f[i][j - 1];
            f[i][j] = (mid != -1 ? f[mid][j - 1] : -1);
        }
    }

    while (q--){
        int x, y;
        cin >> x >> y;
        --x, --y;
        if (x == y){
            cout << 0 << endl;
            continue;
        }
        if (can_switch(x, y)){
            cout << 1 << endl;
            continue;
        }

        int cnt = 2;
        for (int i = 17; i >= 0; i--){
            int to = f[y][i];
            if (to != -1 && l[to] > r[x]){
                cnt += 1 << i;
                y = to;
            }
        }

        y = f[y][0];

        if (y != -1 && can_switch(x, y)){
            cout << cnt << endl;
        } else {
            cout << "impossible" << endl;
        }
    }

}

int main() {
    ios_base::sync_with_stdio(false);

#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif

    solve();

    return 0;
}

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