Submission #1150027

#	Time	Username	Problem	Language	Result	Execution time	Memory
1150027		byunjaewoo	Thousands Islands (IOI22_islands)	C++20	100 / 100	130 ms	32836 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
using namespace std;

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
  vector<multiset<pair<int, int>>> tadj(N);
  vector<set<array<int, 3>>> adj(N);
  vector<vector<pair<int, int>>> radj(N);
  vector<int> ret, st;
  for(int i=0; i<M; i++) tadj[U[i]].insert({V[i], i}), radj[V[i]].push_back({U[i], i});
  queue<int> q;
  auto del=[&]() {
    while(!q.empty()) {
      int curr=q.front(); q.pop();
      for(auto [next, k]:radj[curr]) {
        tadj[next].erase(tadj[next].find({curr, k}));
        if(tadj[next].empty()) q.push(next);
      }
      radj[curr].clear();
    }
  };
  int p=0;
  for(int i=0; i<N; i++) if(tadj[i].empty()) q.push(i);
  del();
  if(tadj[0].empty()) return false;
  while(tadj[p].size()==1) {
    q.push(p), del();
    if(tadj[p].empty()) return false;
    st.push_back(tadj[p].begin()->second);
    p=tadj[p].begin()->first;
  }
  for(int i=0; i<N; i++) if(!tadj[i].empty()) {
    adj[i].insert({tadj[i].begin()->first, tadj[i].begin()->second, 0});
    if(i==p) adj[i].insert({next(tadj[i].begin())->first, next(tadj[i].begin())->second, -1});
  }
  int curr=p, flag=0, t=0, prv=-1;
  do {
    bool flag2=false;
    for(auto [next, k, f]:adj[curr]) if(!f && prv!=k) {
      ret.push_back(k), flag+=1-2*f;
      adj[next].insert({curr, k, 1-f}), adj[curr].erase({next, k, f});
      curr=next, prv=k, flag2=true;
      break;
    }
    if(flag2) continue;
    for(auto [next, k, f]:adj[curr]) if(f && prv!=k) {
      ret.push_back(k), flag+=1-2*f;
      adj[next].insert({curr, k, 1-f}), adj[curr].erase({next, k, f});
      curr=next, prv=k;
      break;
    }
  } while(curr!=p || flag);
  reverse(ret.begin(), ret.end());
  reverse(st.begin(), st.end());
  for(int i:st) ret.push_back(i);
  reverse(ret.begin(), ret.end());
  for(int i:st) ret.push_back(i);
  return ret;
}

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