Submission #576876

#	Time	Username	Problem	Language	Result	Execution time	Memory
576876		wiwiho	Event Hopping (BOI22_events)	C++14	100 / 100	198 ms	26936 KiB

events

#include <bits/stdc++.h>

#define iter(a) a.begin(), a.end()
#define lsort(a) sort(iter(a))
#define gsort(a) sort(iter(a), greater<>())
#define eb emplace_back
#define pob pop_back()
#define ef emplace_front
#define pof pop_front()
#define mp make_pair
#define F first
#define S second
#define uni(a) a.resize(unique(iter(a)) - a.begin())
#define printv(a, b) { \
    for(auto pv : a) b << pv << " "; \
    b << "\n"; \
}

using namespace std;

typedef long long ll;

using pii = pair<int, int>;
using pll = pair<ll, ll>;

struct SparseTable{
    
    vector<vector<pii>> st;
    int n;
    
    SparseTable(vector<pii>& a){
        n = a.size();
        st.resize(20, vector<pii>(n));
        st[0] = a;
        for(int i = 1; i < 20; i++){
            for(int j = 0; j + (1 << i) - 1 < n; j++){
                st[i][j] = min(st[i - 1][j], st[i - 1][j + (1 << (i - 1))]);
            }
        }
    }

    pii query(int l, int r){
        int lg = __lg(r - l + 1);
        return min(st[lg][l], st[lg][r - (1 << lg) + 1]);
    }

};

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

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

    vector<int> l(n + 1), r(n + 1);
    vector<vector<int>> anc(20, vector<int>(n + 1));
    for(int i = 1; i <= n; i++){
        cin >> l[i] >> r[i];
    }
    vector<int> dr = r;
    lsort(dr);
    uni(dr);
    int sz = dr.size();
    vector<pii> mn(sz, mp(INT_MAX, -1));
    for(int i = 1; i <= n; i++){
        int pos = lower_bound(iter(dr), r[i]) - dr.begin();
        mn[pos] = min(mn[pos], mp(l[i], i));
    }
    
    SparseTable st(mn);
    for(int i = 1; i <= n; i++){
        int lp = lower_bound(iter(dr), l[i]) - dr.begin();
        int rp = lower_bound(iter(dr), r[i]) - dr.begin();
        anc[0][i] = st.query(lp, rp).S;
        if(anc[0][i] == i) anc[0][i] = -1;
    }
    
    for(int i = 1; i < 20; i++){
        for(int j = 1; j <= n; j++){
            if(anc[i - 1][j] == -1) anc[i][j] = -1;
            else anc[i][j] = anc[i - 1][anc[i - 1][j]];
        }
    }

    while(q--){

        int s, e;
        cin >> s >> e;
        
        if(s == e){
            cout << "0\n";
            continue;
        }
        if(r[s] > r[e]){
            cout << "impossible\n";
            continue;
        }
    
        int ans = 0;
        int now = e;
        for(int i = 19; i >= 0; i--){
            if(anc[i][now] == -1) continue;
            if(l[anc[i][now]] <= r[s]) continue;
            now = anc[i][now];
            ans += 1 << i;
        }
        if(r[s] < l[now] && anc[0][now] != -1) ans++, now = anc[0][now];
        if(r[s] < l[now]) cout << "impossible\n";
        else cout << ans + 1 << "\n";
    }
    
    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