Submission #639773

#	Time	Username	Problem	Language	Result	Execution time	Memory
639773		study	Thousands Islands (IOI22_islands)	C++17	11.90 / 100	50 ms	16392 KiB

islands

#include <bits/stdc++.h>
#include "islands.h"
using namespace std;
 
const int N = 2e5;
 
vector<int> ans,to[N],canoe[N],prev_all;
deque<pair<int,int>> cycle,prev_cycle;
bitset<N> vu,vu3,path,prev_path,vu2;
bool impo = false, first_cycle = false;
int op1 = 0, op2 = 0, except = 0;
 
bool dfs2(int node){
	if (path[node]){
		op2 = node;
		return true;
	}
	if (vu[node]) return false;
	vu[node] = true;
	path[node] = true;
	for (int i=0; i<to[node].size(); ++i){
		if (!vu3[canoe[node][i]] and (prev_path[canoe[node][i]] or dfs2(to[node][i]))){
			if (prev_path[canoe[node][i]]){
				op2 = canoe[node][i];
				first_cycle = true;
			}
			else cycle.emplace_back(canoe[node][i],node);
			return true;
		}
	}
	path[node] = false;
	return false;
}
 
bool dfs(int node){
//	cout << node << endl;
	if (path[node]){
		op1 = node;
		return true;
	}
	if (vu[node]) return false;
	vu[node] = true;
	path[node] = true;
	for (int i=0; i<to[node].size(); ++i){
		if (!vu3[canoe[node][i]] and dfs(to[node][i])){
			cycle.emplace_back(canoe[node][i],node);
			return true;
		}
	}
	path[node] = false;
	return false;
}
 
void construct(int deb){
//	cout << deb << ' ' << to[deb].size() << endl;
	if (vu2[deb]){
		impo = true;
		return;
	}
	except = deb;
	vu2[deb] = true;
	if (to[deb].empty()){
		impo = true;
		return;
	}
	else if (to[deb].size() == 1){
		vu3[canoe[deb][0]] = true;
		ans.emplace_back(canoe[deb][0]);
		construct(to[deb][0]);
		ans.emplace_back(canoe[deb][0]);
	}
	else{
		int deja_vu = -1;
		bool a = false, b = false;
		for (int j=0; j<2*to[deb].size(); ++j){
			int i = j%to[deb].size();
			if (!a){
				if (dfs(to[deb][i])){
					vu.reset();
					path.reset();
					vector<int> extra;
					prev_all.emplace_back(canoe[deb][i]);
					ans.emplace_back(canoe[deb][i]);
//					for (auto i:cycle) cout << i.first << ' ';
//					cout << endl;
					while (!cycle.empty() and op1 != cycle.back().second){
						extra.emplace_back(cycle.back().first);
						cycle.pop_back();
					}
					prev_cycle = cycle;
					for (int node:extra) ans.emplace_back(node);
					prev_all = extra;
					for (auto node:cycle) prev_all.emplace_back(node.first);
					reverse(cycle.begin(),cycle.end());
					for (auto node:cycle){
						prev_path[node.first] = true;
						ans.emplace_back(node.first);
					}
					reverse(extra.begin(),extra.end());
					for (int node:extra){
						prev_all.emplace_back(node);
						ans.emplace_back(node);
					}
					prev_all.emplace_back(canoe[deb][i]);
					ans.emplace_back(canoe[deb][i]);
					cycle.clear();
					deja_vu = i;
					a = true;
				}
			}
			else if (i != deja_vu){
				if (dfs2(to[deb][i])){
					b = true;
					ans.emplace_back(canoe[deb][i]);
					if (first_cycle){
						reverse(cycle.begin(),cycle.end());
						for (auto i:cycle) ans.emplace_back(i.first);
						reverse(cycle.begin(),cycle.end());
//						cout << op2 << endl;
						while (prev_cycle[0].first != op2){
							prev_cycle.emplace_back(prev_cycle.front());
							prev_cycle.pop_front();
						}
						prev_cycle.emplace_back(prev_cycle.front());
						prev_cycle.pop_front();
						for (auto i:prev_cycle) ans.emplace_back(i.first);
						for (auto i:cycle) ans.emplace_back(i.first);
					}
					else{
						vector<int> extra;
						while (!cycle.empty() and op2 != cycle.back().second){
							extra.emplace_back(cycle.back().first);
							cycle.pop_back();
						}
						for (int node:extra) ans.emplace_back(node);
						reverse(cycle.begin(),cycle.end());
						for (auto i:cycle) ans.emplace_back(i.first);
						reverse(extra.begin(),extra.end());
						for (int node:extra) ans.emplace_back(node);
						ans.emplace_back(canoe[deb][i]);
						for (auto node:prev_all) ans.emplace_back(node);
						ans.emplace_back(canoe[deb][i]);
						reverse(extra.begin(),extra.end());
						for (int node:extra) ans.emplace_back(node);
						reverse(cycle.begin(),cycle.end());
						for (auto node:cycle) ans.emplace_back(node.first);
						reverse(extra.begin(),extra.end());
						for (int node:extra) ans.emplace_back(node);
					}
					ans.emplace_back(canoe[deb][i]);
					break;
				}
			}
		}
		if (!b) impo = true;
	}
}
 
variant<bool,vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V){
	for (int i=0; i<M; ++i){
//		cout << U[i] << ' ' << V[i] << endl;
		to[U[i]].emplace_back(V[i]);
		canoe[U[i]].emplace_back(i);
	}
	construct(0);
	if (impo) return false;
	return ans;
}

Compilation message (stderr)

islands.cpp: In function 'bool dfs2(int)':
islands.cpp:21:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |  for (int i=0; i<to[node].size(); ++i){
      |                ~^~~~~~~~~~~~~~~~
islands.cpp: In function 'bool dfs(int)':
islands.cpp:44:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |  for (int i=0; i<to[node].size(); ++i){
      |                ~^~~~~~~~~~~~~~~~
islands.cpp: In function 'void construct(int)':
islands.cpp:75:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   75 |   for (int j=0; j<2*to[deb].size(); ++j){
      |                 ~^~~~~~~~~~~~~~~~~

• Subtask 1: 1.75 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 0 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 0 / 45