ЗОШ мосты А OK

#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>
#include <string>
#include <stack>
#include <set>
#include <map>
#define pii pair <int,int>
using namespace std;
using ll = long long;
using ld = long double;
void cv(vector <int> &v){
    for (auto x: v) cout<<x<<' ';
    cout<<"\n";
}

void cvl(vector <ll> &v){
    for (auto x: v) cout<<x<<' ';
    cout<<"\n";
}


void cvv(vector <vector <int> > &v){
    for (auto x: v) cv(x);
    cout<<"\n";
}

struct edge{
    int fr, to, id;
};
int n,m;
vector <vector <edge> > G;
const int bl = 2, gr = 1, wh = 0, inf = 2e9;
vector <int>  clr;

void she(edge x){
    cout<<x.fr<<' '<<x.to<<' '<<x.id<<"\n";
}

void shG(){
    for (int i=0;i<n;++i){
        cout<<"i = "<<i<<"\n";
        for (int j = 0; j <G[i].size();++j){she(G[i][j]);}
        cout<<"\n\n";
    }
}
int curT = 0;
vector <edge> bridge; //id мостов
stack <int> comp;
vector <int> tIn, tUp;

void dfs(int v, int parId){//parId - id ребра по которомц пришли в v
    clr[v] = gr;
    tIn[v] = curT++;
    comp.push(v);

    for (auto e: G[v]){
        if (e.id == parId) continue;
        else if (clr[e.to] == wh){
            dfs(e.to, e.id);
            tUp[v] = min(tUp[v], tUp[e.to]);
            if (tUp[e.to] >= tIn[e.to]){
                bridge.push_back(e);
            }
        }
        else if(clr[e.to] == gr){
            tUp[v] = min(tUp[v], tIn[e.to]);
        }

    }
    clr[v] = bl;
}

bool cmp(edge a, edge b){
    return a.id < b.id;
}


int main()
{
    ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>m;
	G.resize(n);
	clr.assign(n, wh);
	tIn.assign(n, inf);
	tUp.assign(n, inf);
	int id = 0;
	for (int i=0;i<m;++i){
            int a,b;
        cin>>a>>b;
        if (a>b) swap(a,b);
        a--; b--;
        edge any;
        any = {a, b, id};
        G[a].push_back(any);
        any = {b, a, id};
        G[b].push_back(any);
        id++;
	}
	//shG();
	for (int i = 0; i < n;++i){
        if (clr[i] == wh){
            dfs(i, -1);
        }
	}
	sort(bridge.begin(), bridge.end(), cmp);
    cout<<bridge.size()<<"\n";
	for (auto i: bridge){
        cout<<i.id+1<<"\n";
        //she(i);
	}
}
/*
13 16
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10
10 11
11 9
11 12
12 13
12 13

13 15
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10
10 11
11 9
11 12
12 13


13 15
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10
10 11
11 9
11 12
12 13

12 14
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10
10 11
11 9
11 12


6 7
1 2
2 3
3 4
1 3
4 5
4 6
5 6


6 8
1 2
2 3
3 4
1 3
4 5
4 6
5 6
1 5

8 10
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8

9 11
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
8 9

10 11
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10

11 12
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10
10 11

11 13
1 2
2 3
3 4
1 3
4 5
4 6
5 6
5 7
5 8
7 8
9 10
10 11
11 9
*/