Submission #1058460

#	Time	Username	Problem	Language	Result	Execution time	Memory
1058460		tolbi	Thousands Islands (IOI22_islands)	C++17	12.35 / 100	21 ms	4788 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
std::variant<bool, std::vector<int>> find_journey(
	int N, int M, std::vector<int> U, std::vector<int> V) {
	vector<vector<pair<int,int>>> arr(N);
	for (int i = 0; i < M; i++){
		arr[U[i]].push_back({V[i],i});
	}
	for (int i = 0; i < N; ++i)
	{
		sort(arr[i].begin(), arr[i].end());
	}
	if (arr[0].size()==0) {
		return false;
	}
	if (arr[0].size()>=2){
		int a = arr[0][0].first;
		int b = arr[0][1].first;
		if (a==b){
			return vector<int>{arr[0][0].second,arr[a][0].second,arr[0][1].second,arr[0][0].second,arr[a][0].second,arr[0][1].second};
		}
		else {
			return vector<int>{
				arr[0][0].second,
				arr[a][0].second,
				arr[0][1].second,
				arr[b][0].second,
				arr[a][0].second,
				arr[0][0].second,
				arr[b][0].second,
				arr[0][1].second
			};
		}
	}
	vector<bool> vis(N,false);
	vector<pair<int,int>> par(N,{-1,-1});
	function<void(int)> dfs = [&](int node)->void{
		if (vis[node]) return;
		vis[node]=true;
		for (auto it : arr[node]){
			if (vis[it.first]) continue;
			par[it.first]={node,it.second};
			dfs(it.first);
		}
	};
	dfs(0);
	for (int i = 1; i < N; i++){
		if (arr[i].size()>=3 && vis[i]){
			vector<int> ans;
			int nd = i;
			while (nd!=-1){
				ans.push_back(par[nd].second);
				nd=par[nd].first;
			}
			reverse(ans.begin(), ans.end());
			sort(arr[i].begin(), arr[i].end(), [&](pair<int,int> a, pair<int,int> b){
				return (par[i].second^1^a.second)>(par[i].second^1^b.second);
			});
			ans.push_back(arr[i][0].second);
			ans.push_back(arr[i][0].second^1);
			ans.push_back(arr[i][1].second);
			ans.push_back(arr[i][1].second^1);
			ans.push_back(arr[i][0].second^1);
			ans.push_back(arr[i][0].second);
			ans.push_back(arr[i][1].second^1);
			ans.push_back(arr[i][1].second);
			nd = i;
			while (nd!=-1){
				ans.push_back(par[nd].second);
				nd=par[nd].first;
			}
			return ans;
		}
	}
	return false;
}

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