Submission #115224

#	Time	Username	Problem	Language	Result	Execution time	Memory
115224		Adhyyan1252	Potemkin cycle (CEOI15_indcyc)	C++11	30 / 100	328 ms	227756 KiB

indcyc

#include<bits/stdc++.h>
#define DEBUG false
using namespace std;

vector<vector<int> > g, h;
int n, r;

vector<int> par;

int find(int cur){
	if(par[cur] == cur) return cur;
	return par[cur] = find(par[cur]);
}

void merge(int a, int b){
	a = find(a);
	b = find(b);
	if(a == b) return;
	par[b] = a;
}

vector<vector<int> > l;
vector<vector<pair<int, int> > >el;


void bfs(int m, int u, int v){
	vector<int> dist(n, INT_MAX);
	vector<int> dpar(n, -1);
	dist[u] = 0;
	queue<int> q; q.push(u);
	while(!q.empty()){
		int top = q.front(); q.pop();
		for(int ad: g[top]){
			if(!((ad == u || ad == v) || (ad != m && !h[ad][m]))) continue;
			if(dist[ad] == INT_MAX){
				dist[ad] = dist[top]+1;
				q.push(ad);
				dpar[ad] = top;
			}
		}
	}
	assert(dist[v] != INT_MAX);
	vector<int> path = {u, m};
	int cur = v;
	while(cur != u){
		path.push_back(cur);
		cur = dpar[cur];
	}
	for(int k: path) cout<<k+1<<" ";
	cout<<endl;
	exit(0);
}
vector<bool> ne;
void rec(vector<int> v, vector<pair<int, int> > e){
	if(v.size() < 4) return;	
	if(DEBUG) cout<<"REC: ";
	if(DEBUG) for(int u: v) cout<<u<<" ";
	if(DEBUG) cout<<endl;
	//reset all the dsu of v
	for(int u: v) par[u] = u;
	
	//select main node, and find neighbors
	int m = v[0];
	for(int u: v){
		if(h[u][m]) ne[u] = true;
		else ne[u] = false;
	}
	ne[m] = true;
	
	if(DEBUG) for(int i = 0; i < n; i++) cout<<i<<" : "<<ne[i]<<endl;
	
	for(pair<int, int> ed: e){
		if(ne[ed.first] || ne[ed.second]) continue;
		merge(ed.first, ed.second);
		if(DEBUG) cout<<"MERGE "<<ed.first<<" , "<<ed.second<<endl;
	}
	
	for(int u: v) l[u].clear();
	for(pair<int, int> ed: e){
		if(ne[ed.first] && !ne[ed.second]){
			int t = find(ed.second);
			l[t].push_back(ed.first);
			if(DEBUG) cout<<"PUSH "<<t<<" "<<ed.first<<endl;
		}else if(!ne[ed.first] && ne[ed.second]){
			int t = find(ed.first);
			l[t].push_back(ed.second);
			if(DEBUG) cout<<"PUSH "<<t<<" "<<ed.second<<endl;
		}
	}
	if(DEBUG) cout<<"REACHED"<<endl;
	//for each l find
	for(int u: v) el[u].clear();
	for(int u: v){
		if(l[u].size() < 2) continue;
		if(DEBUG) cout<<"DOING for "<<u<<endl;
		//do a double loop on all pairs to check if they are adjacent
		for(int i = 0; i < l[u].size(); i++){
			for(int j = i+1; j < l[u].size(); j++){
				if(h[l[u][i]][l[u][j]] == false){
					//found an answer, output it somehow
					//and then exit
					//find shortest path from i to j without having an edge to m
					bfs(m, l[u][i], l[u][j]);
				}else{
					el[u].push_back({l[u][i], l[u][j]});
					if(DEBUG) cout<<"PUSH "<<l[u][i]<<" "<<l[u][j]<<endl;
				}
			}
		}
	}
	if(DEBUG) cout<<"REACHED"<<endl;
	vector<int> nel;
	vector<pair<int, int> > edl;
	for(int u: v){
		if(ne[u] && u != m){
			nel.push_back(u);
		}else{
			l[find(u)].push_back(u);
		}
	}
	for(pair<int, int>& ed: e){
		if(ne[ed.first] == true && ne[ed.second] == false){
			el[find(ed.second)].push_back(ed);
		}else if(ne[ed.first] == false && ne[ed.first] == true){
			el[find(ed.first)].push_back(ed);
		}else if(ne[ed.first] && ne[ed.second]){
			if(ed.first != m && ed.second != m) {
				edl.push_back(ed);
			}
		}else{
			el[find(ed.first)].push_back(ed);
		}
	}
	if(DEBUG) cout<<"REACHED 1"<<endl;
	for(int u: v){
		if(l[u].size() >= 4) rec(l[u], el[u]);
	}
	rec(nel, edl);
	if(DEBUG) cout<<"REACHED 2"<<endl;
}

int main(){
	ios::sync_with_stdio(false); cin.tie(0);
	cin>>n>>r;
	g.resize(n);
	h = vector<vector<int> > (n, vector<int>(n));
	par.resize(n);
	l.resize(n); el.resize(n);
	ne.resize(n);
	
	vector<pair<int, int> > elist(r);
	for(int i = 0; i < r; i++){
		int u, v; cin>>u>>v; u--, v--;
		g[u].push_back(v);
		g[v].push_back(u);
		elist[i] = {u, v};
		h[u][v] = 1; h[v][u] = 1;
	}
	
	vector<int> v;
	for(int i = 0; i < n; i++) v.push_back(i);
	rec(v, elist);
	cout<<"no"<<endl;
}

Compilation message (stderr)

indcyc.cpp: In function 'void rec(std::vector<int>, std::vector<std::pair<int, int> >)':
indcyc.cpp:97:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < l[u].size(); i++){
                  ~~^~~~~~~~~~~~~
indcyc.cpp:98:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = i+1; j < l[u].size(); j++){
                     ~~^~~~~~~~~~~~~

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 10
• Subtask 4: 10 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10
• Subtask 10: 0 / 10