Bridges

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

#define fast ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL)
#define ll long long
#define ld long double
#define pb push_back
#define fe first
#define se second
#define nl "\n"
#define pp pair < ll , ll >
#define sz(x) (ll)x.size()
#define st(x) sort(x.begin(),x.end())
#define rst(x) sort(x.rbegin(), x.rend())
#define all(x) x.begin(),x.end()
long double pi = 3.14159265358979323;

const double EPS = 1e-12;
const int N = 1e6 + 5;
//Just A Gentle Reminder about MOD
const int mod = 1e9 + 7;

//Articulation point

//Two Condn
//1 - if u is root node
//it must have two children components

//2 - not a root
//there should not a back edge from subgraph of v to ancestor of u


vector < ll > v[N];
//vector < ll > ans;
int tin[N];
int low[N]; //earliest node which is back edge
int vis[N];
vector  < pair < int , int > > ans;
ll par[N];
ll timer;

void dfs(ll s , ll timer){

    int cnt = 0 ;
    timer++;
    tin[s] = timer;
    low[s] = timer;
    vis[s] = 1;
    for(auto it : v[s]){


        if(!vis[it]){
            par[it] = s;
            cnt++;
            dfs(it,timer);
            low[s] = min(low[it] , low[s]);

            //if low[it] < tin[s] back edge is present!!
            //condn for no back edge
            if(low[it] > tin[s]){

                ans.push_back({s,it});
            }
        }
        //FOR BACK EDGE
        else if(it != par[s]){
                low[s] = min(tin[it] , low[s]);
        }
    }
    //vis[s] = 2;

}

int main()
{
    fast;
    ll t;
    cin >> t ;
    ll n , m;

    while(t--){
        cin >> n >> m ;
        for(int i = 0 ; i <= n ;i++ ){
            v[i].clear();
            vis[i] = tin[i] = low[i] = par[i] = 0;
        }
        ans.clear();
        timer =  0;
        for(int i = 0 ; i < m ;i++ ){
            ll a , b;
            cin >> a >> b ;
            //cout << a << " " << b << "\n";
            v[a].pb(b);
            v[b].pb(a);
        }
        // for(int i = 1 ; i <= n;  i++ ){
        //  if(!vis[i]){
        //      dfs(i,0);
        //  }
        // }
        dfs(1,0);
        for(auto it : ans){
            cout << it.first << " " << it.second << " ";
        }
    }





















    return 0;
//It's not end it yet
}