Submission #797299

#	Time	Username	Problem	Language	Result	Execution time	Memory
797299		penguinman	Thousands Islands (IOI22_islands)	C++17	27.50 / 100	42 ms	9172 KiB

islands

#include "islands.h"

#include <bits/stdc++.h>
#include <variant>

using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::string;
using ll = int;
using vi = vector<ll>;
using vii = vector<vi>;
using pii = std::pair<ll,ll>;

#define rep(i,j,k) for(ll i=ll(j); i<ll(k); i++)
#define REP(i,j,k) for(ll i=ll(j); i<=ll(k); i++)
#define per(i,j,k) for(ll i=ll(j); i>=ll(k); i--)
#define all(a) a.begin(),a.end()
#define pb emplace_back
#define ln "\n"

struct directed_graph{
  ll N;
  vii edge, revedge;
  vi par;
  vii V;
  directed_graph(vii E){
    N = E.size();
    edge.resize(N);
    revedge.resize(N);
    par.resize(N);
    V.resize(N);
    rep(i,0,N){
      for(auto j: E[i]){
        edge[i].pb(j);
        revedge[j].pb(i);
      }
    }
  }
  vi ord;
  vector<bool> flag;
  void dfs1(ll now){
    flag[now] = true;
    for(auto next: edge[now]){
      if(flag[next]) continue;
      dfs1(next);
    }
    ord.pb(now);
  }
  void dfs2(ll p, ll now){
    flag[now] = true;
    par[now] = p;
    for(auto next: revedge[now]){
      if(flag[next]) continue;
      dfs2(p, next);
    }
  }
  void SCC(){
    flag.resize(N);
    rep(i,0,N){
      if(!flag[i]) dfs1(i);
    }
    reverse(all(ord));
    flag.assign(N,false);
    for(auto el: ord){
      if(!flag[el]){
        dfs2(el,el);
      }
    }
    rep(i,0,N) V[par[i]].pb(i);
  }
};

std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V) {
  vii edge(N), index(N);
  rep(i,0,M){
    edge[U[i]].pb(V[i]);
    index[U[i]].pb(i);
  }
  directed_graph G(edge);
  G.SCC();
  ll good = -1;
  vi ans;
  {
    std::queue<ll> que;
    que.push(0);
    vi flag(N);
    vi rev(N,-1);
    vi idx(N);
    flag[0] = true;
    rev[0] = 0;
    while(!que.empty()){
      ll now = que.front(); que.pop();
      if(G.V[G.par[now]].size() >= 2 && edge[now].size() >= 2){
        good = now;
        while(now != 0){
          ans.pb(idx[now]);
          now = rev[now];
        }
        reverse(all(ans));
        break;
      }
      rep(i,0,edge[now].size()){
        ll next = edge[now][i];
        if(flag[next]) continue;
        flag[next] = true;
        rev[next] = now;
        idx[next] = index[now][i];
        que.push(next);
      }
    }
  }
  if(good != -1){
    std::set<ll> used;
    for(auto el: ans){
      used.insert(el);
      used.insert(el^1);
    }
    std::queue<ll> que;
    que.push(good);
    vi rev(N,-1);
    vi idx(N);
    rev[good] = good;
    while(!que.empty()){
      ll now = que.front(); que.pop();
      rep(i,0,edge[now].size()){
        ll next = edge[now][i];
        if(rev[next] != -1) continue;
        if(used.count(index[now][i])) continue;
        rev[next] = now;
        idx[next] = index[now][i];
        que.push(next);
      }
    }
    rep(i,0,N){
      if(rev[i] != -1){
        vi ans2;
        rep(j,0,edge[i].size()){
          if(used.count(index[i][j])) continue;
          ll next = edge[i][j];
          if(next == good){
            ans2.pb(index[i][j]);
            break;
          }
        }
        if(ans2.empty()) continue;
        ll now = i;
        while(now != good){
          ans2.pb(idx[now]);
          now = rev[now];
        }
        ll len = ans.size();
        reverse(all(ans2));
        for(auto el: ans2) ans.pb(el);
        for(auto el: ans2) ans.pb(el^1);
        reverse(all(ans2));
        for(auto el: ans2) ans.pb(el);
        for(auto el: ans2) ans.pb(el^1);
        per(i,len-1,0) ans.pb(ans[i]);
        return ans;
      }
    }
  }
  return false;
  
}

• Subtask 1: 1.75 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 0 / 21
• Subtask 4: 24 / 24
• Subtask 5: 0 / 45