Submission #1227204

#	Time	Username	Problem	Language	Result	Execution time	Memory
1227204		brinton	Thousands Islands (IOI22_islands)	C++20	9.10 / 100	58 ms	11592 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) {
  auto co = [](int id){
    if(id%2 == 0) return id+1;
    else return id-1;
  };

  vector<set<pair<int,int>>> edges(N);// nxt,id
  for(int i = 0;i < M;i++){
    edges[U[i]].insert({V[i],i});
  }
  // if(edges[0].size() < 2) return false;
  vector<int> ans;
  vector<bool> vis(N,false);
  
  int root = 0;
  vector<int> to_root;
  while(edges[root].size() <= 1){
    if(edges[root].size() == 0) return false;
    auto [nxt,id] = *edges[root].begin();

    to_root.push_back(id);
    vis[root] = true;
    edges[root].erase({nxt,id});
    edges[nxt].erase({root,co(id)});

    root = nxt;
  }
  // cout << "!" << root << endl;
  function<void(int)> dfs = [&](int cur){
    // cout << "?" << cur << endl;
    vis[cur] = true;
    if(cur == root){
      vis[edges[cur].begin()->first] = true;
    }
    for(auto [nxt,id]:edges[cur]){
      if(vis[nxt]) continue;
      ans.push_back(id);
      dfs(nxt);
      ans.push_back(co(id));
    }
    if(cur == root){
      auto [nxt,id] = *edges[cur].begin();
      ans.push_back(id);
      dfs(nxt);
      ans.push_back(co(id));
    }
  };
  dfs(root);
  // for(int i = 0;i < N;i++) cout << vis[i] << " ";cout << endl;
  // for(int i = 0;i < N;i++) if(!vis[i]) return false;
  
  int csz = ans.size();

  for(int i = 0;i < csz;i++) ans.push_back(co(ans[i]));
  
  vector<int> ret = to_root;
  for(auto &i:ans) ret.push_back(i);
  for(int i = to_root.size()-1;i >= 0;i--) ret.push_back(to_root[i]);

  return ret;
  // return ans;
}

• Subtask 1: 0 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45