Reforma Grafos.cpp

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5+10;
vector<int> grafo[maxn];
vector<pair<int,int>> arestas;
set<pair<int,int>> usadas;
bool mark[maxn];
void dfs(int u){
    mark[u] = 1;
    for(int i=0; i<grafo[u].size(); i++){
        int v = grafo[u][i];
        if(mark[v] and usadas.find({u, v}) == usadas.end()){
            arestas.push_back({u, v});
            usadas.insert({u, v});
            usadas.insert({v, u});
            continue;
        }
        else if(mark[v]) continue;
        usadas.insert({u, v});
        usadas.insert({v, u});
        dfs(v);
    }
}
int main(){
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
    int n, m;
    cin >> n >> m;
    for(int i=1; i<=m; i++){
        int u, v;
        cin >> u >> v;
        grafo[u].push_back(v);
        grafo[v].push_back(u);
    }
    dfs(1);
    cout << arestas.size() << "\n";
    for(int i=0; i<arestas.size(); i++){
        cout << arestas[i].first << " " << arestas[i].second << "\n";
    }
    return 0;
}