Submission #1258617

#	Time	Username	Problem	Language	Result	Execution time	Memory
1258617		mquang	Potemkin cycle (CEOI15_indcyc)	C++20	100 / 100	386 ms	118212 KiB

indcyc

#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
using namespace std;

void input(){
	#define taskname ""
	if(fopen(taskname ".inp", "r")){
		freopen(taskname ".inp", "r", stdin);
		freopen(taskname ".out","w",stdout);
	}
}
const int N = 1e3+1;
const int INF =1e9+7;
ll n,m;
vector<vector<ll>>g(N);
vector<vector<ll>>col(N,vector<ll>(N,0));
vector<vector<pair<ll,ll>>>par(N,vector<pair<ll,ll>>(N));
void sub1(){
	vector<vector<bool>>hw(n+1,vector<bool>(n+1,0));
	for(ll i=0;i<m;++i){
		ll u,v;
		cin >> u >> v;
		g[u].push_back(v);
		g[v].push_back(u);
		hw[u][v] = 1;
		hw[v][u] = 1;
	}
	bool f =0;
//	for(auto x : g[1]) cout << x << " ";
//	cout << endl;
	for(ll mask =0;mask < (1 << n);++mask){
		if(__builtin_popcount(mask) < 4) continue;
		vector<ll>pth;
		for(ll i=1;i<=n;++i){
			if((mask >> (i-1)) & 1) pth.push_back(i);
		}
		bool br = 0;
		ll sz = pth.size();
		for(ll i=0;i<pth.size();++i){
			ll j = (i + 2) % sz;
			while(1){
				if(hw[pth[i]][pth[j]]){
					br = 1;
					break;
				}
				if(br) break;
				++j;
				j %= sz;
				if(i == 0 && j == sz-1) break;
				if(j == i-1) break;
			}
			if(br) break;
		}
		if(br) continue;
			bool ck = 0;
			vector<bool>vis(n+1,0);
			ll i=0;
//			for(auto x : pth) cout << x << " ";
//			cout << endl;
			while(1){
//				cout << i << endl;
				bool ok = 0;
				for(auto x : g[pth[i]]){
//					if(!ck) break;
					if(x == pth[(i+1)%sz] && !vis[x]){
						++i;
						vis[x] = 1;
						ok = 1;
						break;
					}
				}
				if(!ok) break;
				if(i == sz){
					ck = 1;
					break;
				}
			}
			if(ck){
				f = 1;
				for(auto x : pth) cout << x << " ";
				cout << '\n';
				break;
			}
	}
	if(!f) cout << "no" << '\n';
}
bool dfs(pair<ll,ll> cur,vector<vector<vector<pair<ll,ll>>>>& g){
	ll u = cur.first, v = cur.second;
	col[u][v] = 1;
	for(auto x : g[u][v]){
		ll u1 = x.first, v1 = x.second;
		if(col[u1][v1] == 0){
			par[u1][v1] = {u,v};
			if(dfs(x,g)) return 1;
		}
		else if(col[u1][v1] == 1) return 1;
	}
	col[u][v] = 2;
	return 0;
}
void sub4(){
    vector<unordered_set<int>> adj(n+1);
    vector<pair<int,int>> ed;
    ed.reserve(m);
    for(int i = 0; i < m; ++i){
        int u, v;
        cin >> u >> v;
        adj[u].insert(v);
        adj[v].insert(u);
        ed.push_back({u, v});
    }
    vector<pair<int,int>> canh;
    for(auto &e : ed){
        canh.push_back({e.first, e.second});
        canh.push_back({e.second, e.first});
    }
    int sz = canh.size();
    vector<vector<int>> pos(n+1);
    for(int i = 0; i < sz; ++i) pos[canh[i].first].push_back(i);
    vector<vector<int>> g(sz);
    for(int i = 0; i < sz; ++i){
        int u = canh[i].first;
        int v = canh[i].second;
        for(int jid : pos[v]){
            int w = canh[jid].second;
            if(w == u) continue; 
            if(adj[u].count(w) == 0) g[i].push_back(jid);
        }
    }
    vector<int> col(sz, 0), par(sz, -1);
    bool kt = 0;
    vector<int> ct;
    for(int s = 0; s < sz && !kt; ++s){
        if(col[s] != 0) continue;
        vector<pair<int,int>> stk;
        stk.push_back({s, 0});
        col[s] = 1;
        par[s] = -1;
        while(!stk.empty() && !kt){
            int node = stk.back().first;
            int &it = stk.back().second;
            if(it < g[node].size()){
                int to = g[node][it++];
                if(col[to] == 0){
                    par[to] = node;
                    col[to] = 1;
                    stk.push_back({to, 0});
                } 
				else if(col[to] == 1){
                    vector<int> idxs;
                    int cur = node;
                    idxs.push_back(cur);
                    while(cur != to){
                        cur = par[cur];
                        if(cur == -1) break;
                        idxs.push_back(cur);
                    }
                    if(cur == -1) continue;
                    reverse(idxs.begin(), idxs.end());
                    vector<int> ans;
                    ans.push_back(canh[idxs[0]].first);
                    for(int t = 0; t < idxs.size(); ++t) ans.push_back(canh[idxs[t]].second);
                    if(ans.size() > 1 && ans.front() == ans.back()) ans.pop_back();
                    if(ans.size() >= 4){
                        unordered_set<int> seen;
                        bool ok = true;
                        for(int x : ans){
                            if(seen.count(x)){ 
								ok = false; 
								break;
							}
                            seen.insert(x);
                        }
                        if(ok){
                            ct = ans;
                            kt = true;
                            break;
                        }
                    }
                }
            } 
			else{
                col[node] = 2;
                stk.pop_back();
            }
        }
    }
    if(!kt){
        cout << "no";
        return;
    }
    for(int i = 0; i < ct.size(); ++i) cout << ct[i] << ' ';
}
int main(){
	cin.tie(0)->sync_with_stdio(0);
	input();
	cin >> n >> m;
	//if(n <= 1 && m  <= 45) sub1();
	//else sub4();
	sub4();
	return 0;
}
/*
4 5
1 2
2 3
3 4
4 1
1 3
*/

Compilation message (stderr)

indcyc.cpp: In function 'void input()':
indcyc.cpp:10:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   10 |                 freopen(taskname ".inp", "r", stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
indcyc.cpp:11:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   11 |                 freopen(taskname ".out","w",stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

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