Submission #837061

#	Time	Username	Problem	Language	Result	Execution time	Memory
837061		APROHACK	Thousands Islands (IOI22_islands)	C++17	55 / 100	65 ms	38508 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
#define pb push_back
#define ll long long
#define ff first
#define ss second
#include <variant>
#include <vector>
using namespace std;
vector<pair<int, int > >child[5005];
int devuelta[200005];
vector<pair<int, int > > adj[5005];
vector<int>tempRoute;
vector<int>rt;
bool dfs(int node, int parent){
	//cout << " at node " << node << endl;
	for(int i = 0 ; i < adj[node].size() ; i ++){
		if(adj[node][i].ff == parent)continue;
		child[node].pb(adj[node][i]);
	}
	if(child[node].size() >= 2){

			int a = child[node][0].ss;
			int b = devuelta[child[node][0].ss]; 
			int c =	child[node][1].ss; 
			int d = devuelta[c];
			tempRoute = {a, b, c, d, b, a, d, c};
			return true;
	}
	for(auto i : child[node]){
		if(dfs(i.ff, node)){
			rt.pb(i.ss);
			return true;
		}
	}
	return false;
}
int  vis[5005];
#define ancestor 1
#define past 2
#define unvisited -1
int used[5005];
bool isCycle[5005];
vector<int>lastNodes;
vector<int>ciclo, ejesCiclo[2], cicloCompleto;
vector<int>finalRoute;
vector<int>finalReal;
bool dfs2(int node){
	//cout << " at " << node << endl;
	finalRoute.pb(node);	
	vis[node] = ancestor;
	for(int i = 0 ; i < adj[node].size() ; i ++){
		if(adj[node][i].ss % 2 == 1)continue;	
		if(vis[adj[node][i].ff] == ancestor){
			used[node] = adj[node][i].ss;
			//cout << "found cicle: " << endl; 
			while(finalRoute.back() != adj[node][i].ff){
				ciclo.pb(finalRoute.back());
				finalRoute.pop_back();
			}	
			ciclo.pb(finalRoute.back());
			finalRoute.pop_back();
			for(auto j : ciclo)isCycle[j] = true;
			reverse(ciclo.begin(), ciclo.end());
			for(auto j : ciclo){
				ejesCiclo[0].pb(used[j]);
				//cout << "eje ciclo " << used[j] << endl;
				ejesCiclo[1].pb(used[j]+1);
			}	
			cicloCompleto = ejesCiclo[0];
			for(auto j : ejesCiclo[1])cicloCompleto.pb(j);
			vector<int>aux = ejesCiclo[0];
			reverse(aux.begin(), aux.end());
			for(auto j : aux)cicloCompleto.pb(j);
			aux = ejesCiclo[1];
			reverse(aux.begin(), aux.end());
			for(auto j : aux)cicloCompleto.pb(j);
			return true;
		}
	}

	for(int i = 0 ; i < adj[node].size() ; i ++){
		if(adj[node][i].ss % 2 == 1)continue;
		if(vis[adj[node][i].ff] == past)continue;
		// this is unvisited
		used[node] = adj[node][i].ss;
		if(dfs2(adj[node][i].ff)){
			if(!isCycle[node]){
				finalReal.pb(adj[node][i].ss);
			}
			return true;
		}
	}
	vis[node] = past;
	finalRoute.pop_back();
	return false;
}
std::variant<bool, std::vector<int>> find_journey(
	int N, int M, std::vector<int> U, std::vector<int> V) {
	int cuenta[N][N];

	vector<int>parejas[N][N];
	for(int i = 0 ; i < N ; i ++){
		for(int j = 0 ; j < N ; j ++){
			cuenta[i][j] = 0;
		}
	}
	for(int i = 0 ; i < M ; i ++ ){
		cuenta[U[i]][V[i]] ++  ;
		parejas[U[i]][V[i]].pb(i);
		adj[U[i]].pb({V[i], i});
	}

	if (N == 2) {
		if(cuenta[0][1] >= 2 and cuenta[1][0] >= 1){

			int a = parejas[0][1][0];
			int b = parejas[1][0][0];
			int c = parejas[0][1][1];
			vector<int>ans = {a, b, c, a, b, c};
			return ans; 
		}
		return false;
  	}else{
		bool case3 = true;
		bool case4 = true;
		if( M % 2 == 1){
			case3 = false;
			case4 = false;
		}
		
		if(case3 or case4){
			for(int i = 0 ; i < M ; i += 2){
				if(U[i] != V[i+1] or V[i] != U[i+1] )case3 = false;	
				if(U[i] != U[i+1] or V[i] != V[i+1] )case4 = false;
				devuelta[i] = i+1;
				devuelta[i+1] = i;
			}
		}
		if(!case3 and !case4){
			//cout << "wrong case : " << endl;	
			int a = parejas[0][1][0];
			int b = parejas[1][0][0];
			int c = parejas[0][2][0];
			int d = parejas[2][0][0];
			vector<int>ans = {a, b, c, d, b, a, d, c};
			return ans;
		}else if(case3){
			//cout << "case 3 " << endl;
			if(!dfs(0, -1))return false;
			vector<int>ans = rt;
			reverse(ans.begin(), ans.end());
			for(auto i : tempRoute)ans.pb(i);
			for(auto i : rt)ans.pb(i);
			return ans;
		}else{
			//cout << " ! " << endl;
			for(int i = 0 ; i < 5005 ; i ++)vis[i] = unvisited;
			if(!dfs2(0))return false;
			vector<int>ans;
			reverse(finalReal.begin(), finalReal.end());
			ans = finalReal;
			for(auto i : cicloCompleto)ans.pb(i);
			reverse(finalReal.begin(), finalReal.end());
			for(auto j : finalReal)ans.pb(j);
			return ans;
		}
	}
}

Compilation message (stderr)

islands.cpp: In function 'bool dfs(int, int)':
islands.cpp:17:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |  for(int i = 0 ; i < adj[node].size() ; i ++){
      |                  ~~^~~~~~~~~~~~~~~~~~
islands.cpp: In function 'bool dfs2(int)':
islands.cpp:52:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   52 |  for(int i = 0 ; i < adj[node].size() ; i ++){
      |                  ~~^~~~~~~~~~~~~~~~~~
islands.cpp:82:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   82 |  for(int i = 0 ; i < adj[node].size() ; i ++){
      |                  ~~^~~~~~~~~~~~~~~~~~

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