Submission #1058401

#	Time	Username	Problem	Language	Result	Execution time	Memory
1058401		fuad27	Thousands Islands (IOI22_islands)	C++17	10 / 100	21 ms	9284 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>>> g(N);
	for(int i = 0;i<M;i++) {
		g[U[i]].push_back({V[i],i});
	}
	bool subt2=1;
	{
		vector<vector<int>> a(N, vector<int>(N, -1));
		for(int i = 0;i<M;i++) {
			a[U[i]][V[i]] = i;
		}
		for(int i= 0;i<N;i++) {
			for(int j = 0;j<N;j++) {
				if(i==j)continue;
				if(a[i][j]==-1)subt2=false;
			}
		}
		if(M!=N*(N-1))subt2=false;
	}
	if(N == 2) {
		if(g[0].size() < 2)return false;
		if(g[1].size() == 0)return false;
		vector<int> v;
		v.push_back(g[0][0].second);
		v.push_back(g[1][0].second);
		v.push_back(g[0][1].second);
		v.push_back(g[0][0].second);
		v.push_back(g[1][0].second);
		v.push_back(g[0][1].second);
		return v;
	}
	else if(subt2) {
		if(N <= 2) {
			return false;
		}
		vector<vector<int>> a(N, vector<int>(N, -1));
		for(int i = 0;i<M;i++) {
			a[U[i]][V[i]] = i;
		}
		vector<int> ans={a[0][1], a[1][2], a[2][1], a[0][1], a[0][2], a[1][2], a[2][1], a[0][2]};
		return ans;
	}
	else {
		vector<int> topo;
		vector<bool> vis(N);
		int timer = 0;
		vector<int> tin(N), tout(N);
		bool check=false;
		auto dfs = [&](int at, auto &&dfs) -> void {
			vis[at]=1;
			tin[at] = ++timer;
			for(auto [to,w]:g[at]) {
				if(!vis[to])
					dfs(to, dfs);
			}
			tout[at] =  ++timer;
		};
		auto dfs2 = [&](int at, int par, auto &&dfs2) -> void {
			vis[at]=1;
			for(auto [to,w]:g[at]) {
				if(!vis[to])
					dfs2(to, at, dfs2);
				else if(vis[to]) {
					if(to!=par and tin[to] <= tin[at] and tout[at] <= tout[to]) 
						check=true;
				}
			}
		};
		for(int i= 0;i<N;i++) {
			if(!vis[i])
				dfs(i, dfs);
		}
		vis.assign(N, 0);
		for(int i= 0;i<N;i++) {
			if(!vis[i])
				dfs2(i, -1, dfs2);
		}
		return check;
	}
	return false;
}

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