Submission #579716

#	Time	Username	Problem	Language	Result	Execution time	Memory
579716		jasmin	Event Hopping (BOI22_events)	C++17	0 / 100	340 ms	55392 KiB

events

#include<bits/stdc++.h>
using namespace std;
#define int long long

const int inf=1e18;
vector<int> tin;
vector<int> tout;
int t=0;

void dfs(int v, vector<bool>& vis, vector<vector<int> >& adi){
    if(vis[v]) return;
    vis[v]=true;
    tin[v]=t;
    t++;

    for(auto u: adi[v]){
        dfs(u, vis, adi);
    }

    tout[v]=t;
    t++;
}

bool ancestor(int a, int b){
    return tin[a]<tin[b] && tout[b]<tout[a];
}

int dist(int a, int b, vector<vector<int> >& up, int l){
    if(a==b) return 0;
    if(!ancestor(b, a)) return inf;

    int ans=0;
    //cout << "dist: " << a << " " << b << " " << ancestor(b, a) << "\n";
    for(int x=l-1; x>=0; x--){
        if(up[a][x]!=-1 && ancestor(b, up[a][x])){
            ans+=(1<<x);
            a=up[a][x];
            //cout << a << " " << b << "\n" << flush;
        }
    }
    assert(up[a][0]==b);
    return ans+1;
}

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

    int n, q;
    cin >> n >> q;
    vector<pair<int,int> > e(n);
    map<int, pair<vector<int>, vector<int> > > time;
    for(int i=0; i<n; i++){
        int s, t;
        cin>> s >> t;
        e[i]={s, t};
        time[s].first.push_back(i);
        time[t].second.push_back(i);
    }

    vector<vector<int> > adi(n);
    vector<int> p(n, -1);
    set<int> active;
    for(auto m: time){
        for(auto e: m.second.first){
            active.insert(e);
        }
        
        for(auto e: m.second.second){
            for(auto x: active){
                if(x==e) continue;
                p[e]=x;
                adi[x].push_back(e);
            }
        }
        for(auto e: m.second.second){
            active.erase(e);
        }
    }

    /*for(int i=0; i<n; i++){
        for(auto e: adi[i]){
            cout << e << " ";
        }
        cout << "\n" << flush;
    }*/

    int l=25;
    vector<vector<int> > up(n, vector<int> (l, -1));
    for(int i=0; i<n; i++){
        up[i][0]=p[i];
    }
    for(int x=1; x<l; x++){
        for(int i=0; i<n; i++){
            if(up[i][x-1]!=-1){
                up[i][x]=up[up[i][x-1]][x-1];
            }
        }
    }


    tin.resize(n, inf);
    tout.resize(n, inf);
    vector<bool> vis(n);
    for(int i=0; i<n; i++){
        if(p[i]==-1){
            //cout << "start: " << i << "\n" << flush;
            dfs(i, vis, adi);
        }
    }
    /*cout << "achtung:\n";
    for(int i=0; i<n; i++){
        cout << tin[i] << " " << tout[i] << "\n" << flush;
    }*/

    for(int i=0; i<q; i++){
        int a, b;
        cin >> a >> b;
        if(e[a-1].second==e[b-1].second){
            cout << 1 << "\n";
            continue;
        }

        int ans=dist(a-1, b-1, up, l);
        if(ans==inf){
            cout << "impossible\n";
        }
        else{
            cout << ans << "\n";
        }
    }
}

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