Submission #1120957

#	Time	Username	Problem	Language	Result	Execution time	Memory
1120957		Wansur	Event Hopping (BOI22_events)	C++17	70 / 100	1126 ms	320684 KiB

events

#include <bits/stdc++.h>
#define f first
#define s second
#define ent '\n'
#define int long long

typedef long long ll;
using namespace std;
const int maxn = 2e5 + 12;
const int mod = 1e9 + 7;

vector<int> g[maxn];
int d[maxn];
int up[20][maxn];
int sup[20][maxn];
int ans[5005][5005];
int l[maxn], r[maxn];
int n, q;

void solve5000(vector<pair<int, int>> u) {
    for(int j = 1; j <= n; j++) {
        pair<int, int> mx = {-1, -1};
        for(auto [x, pos] : u) {
            if(pos < 0) {
                if(r[-pos] > r[j]) continue;
                mx = max(mx, {r[-pos], -pos});
            }
            else {
                if(r[pos] > r[j]) continue;
                g[mx.second].push_back(pos);
            }
        }
        queue<int> q;
        for(int i = 1; i <= n; i++) {
            ans[i][j] = 1e9;
        }
        ans[j][j] = 0;
        q.push(j);
        for(int i = 1; i <= n; i++) {
            if(r[i] >= l[j] && r[i] <= r[j] && i != j) {
                q.push(i);
                ans[i][j] = 1;
            }
        }
        while(q.size()) {
            int v = q.front();
            q.pop();
            for(int to : g[v]) {
                if(ans[to][j] > ans[v][j] + 1) {
                    ans[to][j] = ans[v][j] + 1;
                    q.push(to);
                }
            }
        }
        for(int i = 1; i <= n; i++) {
            g[i].clear();
        }
    }
    while(q--) {
        int i, j;
        cin >> i >> j;
        if(ans[i][j] > n) {
            cout << "impossible\n";
        }
        else {
            cout << ans[i][j] << ent;
        }
    }
}

void solve() {
    cin >> n >> q;
    vector<pair<int, int>> u;
    for(int i = 1; i <= n; i++) {
        cin >> l[i] >> r[i];
        u.push_back({l[i], -i});
        u.push_back({r[i], i});
    }
    sort(u.begin(), u.end());
    if(n <= 5000) {
        solve5000(u);
        return;
    }
    if(q > 100) {
        pair<int, int> mx = {-1, -1}, smx = mx;
        for(auto [x, pos] : u) {
            if(pos < 0) {
                pair<int, int> tx = {r[-pos], -pos};
                if(tx > mx) {
                    smx = mx;
                    mx = tx;
                }
                else if(tx > smx) {
                    smx = tx;
                }
            }
            else {
                up[0][pos] = mx.second;
                sup[0][pos] = smx.second;
            }
        }
        for(int k = 1; k < 20; k++) {
            for(int i = 1; i <= n; i++) {
                up[k][i] = up[k - 1][up[k - 1][i]];
                sup[k][i] = sup[k - 1][sup[k - 1][i]];
            }
        }
        while(q--) {
            int i, j;
            cin >> i >> j;
            int ans = 0;
            for(int k = 19; k >= 0; k--) {
                if(up[k][i] != 0 && r[up[k][i]] < l[j]) {
                    i = up[k][i];
                    ans += (1 << k);
                }
            }
            if(i == j) {
                cout << "0\n";
            }
            else if(r[i] >= l[j] && r[i] <= r[j]) {
                cout << "1\n";
            }
            else if(up[0][i] == 0 || r[up[0][i]] < l[j] || ans > n || r[i] > r[j]) {
                cout << "impossible\n";
            }
            else if(r[up[0][i]] > r[j]) {
                for(int k = 19; k >= 0; k--) {
                    if(sup[k][i] != 0 && r[up[k][i]] < l[j]) {
                        i = sup[k][i];
                        ans += (1 << k);
                    }
                }
                ans++;
                i = sup[0][i];
                if(i != j) {
                    if(l[j] <= r[i] && r[i] <= r[j]) {
                        ans++;
                    }
                    else {
                        cout << "impossible\n";
                        continue;
                    }
                }
                cout << ans << ent;
            }
            else {
                i = up[0][i];
                ans++;
                ans += (i != j);
                cout << ans << ent;
            }
        }
        return;
    }

    while(q--) {
        int i, j;
        cin >> i >> j;
        if(r[i] > r[j]) {
            cout << "impossible\n";
            continue;
        }
        if(i == j) {
            cout << "0\n";
            continue;
        }
        int ans = 0;
        pair<int, int> mx = {-1, -1};
        for(auto [x, pos] : u) {
            if(pos < 0) {
                if(r[-pos] > r[j]) continue;
                mx = max(mx, {r[-pos], -pos});
            }
            else {
                up[0][pos] = mx.second;
            }
        }
        for(int _ = 0; _ <= n && r[i] < l[j]; _++) {
            ans++;
            i = up[0][i];
        }
        if(ans > n) {
            cout << "impossible\n";
        }
        else {
            if(i != j) ans++;
            cout << ans << ent;
        }
    }

}

signed main(){

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;

//    cin >> t;
    while(t--){
        solve();
    }
}

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