Created
August 19, 2021 22:01
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#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; | |
} |
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