This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
//#define int long long
#define ff first
#define ss second
#define pb push_back
#define all(x) x.begin(),x.end()
using namespace std;
const int N=1e5+5;
int p[2][N],vis[N],tin[N],low[N];
vector <int> g[N];
int find_set(int i,int v){
if(p[i][v]==v)return v;
return p[i][v]=find_set(i,p[i][v]);
}
bool union_set(int i,int u,int v){
if(find_set(i,u)==find_set(i,v))return false;
p[i][u]=v;
return true;
}
int t=0;
void dfs(int v,int p){
vis[v]=1;
t++;
tin[v]=t;
low[v]=t;
for(auto to : g[v]){
if(to!=p){
if(vis[to])low[v]=min(low[v],tin[to]);
else{
dfs(to,v);
low[v]=min(low[v],low[to]);
if(low[to]>tin[v]){
cout<<v<<" "<<to<<"\n";
}
}
}
}
}
signed main(){
ios_base::sync_with_stdio();
cin.tie(0);cout.tie(0);
int n,m;
cin>>n>>m;
for(int i=1;i<=n;i++){
p[0][i]=i;
p[1][i]=i;
}
for(int i=0;i<m;i++){
int u,v;
cin>>u>>v;
if(union_set(0,u,v)){
g[u].pb(v);
g[v].pb(u);
}
else if(union_set(1,u,v)){
g[u].pb(v);
g[v].pb(u);
}
}
for(int i=1;i<=n;i++){
sort(all(g[i]));
for(int j=1;j<g[i].size();j++){
if(g[i][j]==g[i][j-1]){
g[i][j]=0;
g[i][j-1]=0;
}
}
}
for(int i=1;i<=n;i++){
if(!vis[i])dfs(i,0);
}
}
Compilation message (stderr)
pipes.cpp: In function 'int main()':
pipes.cpp:64:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
64 | for(int j=1;j<g[i].size();j++){
| ~^~~~~~~~~~~~
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