Submission #603307

#	Time	Username	Problem	Language	Result	Execution time	Memory
603307		DanerZein	Event Hopping (BOI22_events)	C++14	20 / 100	1579 ms	40380 KiB

events

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
typedef pair<ii,int> iii;
typedef vector<ii> vii;
typedef vector<int> vi;
const int MAX_N=1e5+10;
const int MAX=1e9;
vector<vi> G;
vector<vii> que;
vii ev;
int dis[MAX_N];
int n;
bool isq[MAX_N];
void bfs(int u){
  for(int i=0;i<n;i++) dis[i]=MAX;
  dis[u]=0; isq[u]=1;
  queue<int> q; q.push(u);
  while(!q.empty()){
    int x=q.front(); q.pop();
    isq[x]=0;
    for(auto &v:G[x]){
      if(dis[v]>dis[x]+1){
	dis[v]=dis[x]+1;
	if(!isq[v]){
	  isq[v]=1;
	  q.push(v);
	}
      }
    }
  }
}
int in[MAX_N];
int pa[MAX_N][32];
int le[MAX_N];
void dfs(int u,int p){
  pa[u][0]=p;
  for(int i=1;i<=20;i++){
    pa[u][i]=pa[pa[u][i-1]][i-1];
  }
  for(auto &v:G[u]){
    if(v!=p) {
      le[v]=le[u]+1;
      dfs(v,u);
    }
  }
}
int father(int u,int v){
  int dif=le[u]-le[v];
  if(dif<0) return -1;
  for(int i=0;i<=20;i++){
    if(dif&(1<<i)) u=pa[u][i];
  }
  if(u!=v) return -1;
  return dif;
}
int con[MAX_N];
int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL); cout.tie(NULL);
  int q; cin>>n>>q;
  bool t2=0;
  if(n<=1000 && q<=100) t2=1;
  vii enp;
  for(int i=0;i<n;i++){
    int a,b; cin>>a>>b;
    ev.push_back(ii(a,b));
    enp.push_back(ii(b,i));
    con[i]=i;
  }
  G.resize(n+1);
  if(t2){
    for(int i=0;i<n;i++){
      for(int j=0;j<n;j++){
	if(ev[j].first<=ev[i].second && ev[i].second<=ev[j].second){
	  G[i].push_back(j);
	}
      }
    }
  }
  else{
    sort(enp.begin(),enp.end());
    for(int i=0;i<n-1;i++){
      if(enp[i].first==enp[i+1].first){
	con[enp[i].second]=enp[i+1].second;
	con[enp[i+1].second]=enp[i].second;
      }
    }
    for(int i=0;i<n;i++){
      auto it=lower_bound(enp.begin(),enp.end(),ii(ev[i].first,0));
      int l=it-enp.begin();
      it=upper_bound(enp.begin(),enp.end(),ii(ev[i].second+1,0));
      int r=it-enp.begin();
      for(int j=l;j<r;j++){
	if(i!=enp[j].second){
	  G[i].push_back(enp[j].second);
	  in[enp[j].second]=1;
	}
      }
    }
    for(int i=0;i<n;i++){
      if(!in[i] || con[i]!=i){
	dfs(i,i);
      }
    }
  }
  int iq=0;
  que.resize(n);
  while(q--){
    int s,e; cin>>s>>e;
    s--; e--;
    if(t2){
      que[s].push_back(ii(e,iq));
      iq++;
    }
    else{
      int ans=father(s,e);
      if(ans!=-1) cout<<ans<<endl;
      else{
	int ca=father(s,con[e])+1;
	if(ca!=0) cout<<ca<<endl;
	else
	  cout<<"impossible\n";
      }
    }
  }
  if(t2){
    vector<int> ans(iq);
    for(int i=0;i<n;i++){
      bfs(i);
      for(auto &v:que[i]){
	int s=i; int e=v.first;
	bfs(s);
	if(dis[e]>=MAX) ans[v.second]=-1;
	else ans[v.second]=dis[e];
      }
    }
    for(int i=0;i<ans.size();i++){
      if(ans[i]==-1) cout<<"impossible\n";
      else cout<<ans[i]<<endl;
    }
  }
}

Compilation message (stderr)

events.cpp: In function 'int main()':
events.cpp:139:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  139 |     for(int i=0;i<ans.size();i++){
      |                 ~^~~~~~~~~~~

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