389.cpp

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <fstream>

using namespace std;

typedef long long int lli;
typedef unsigned long long ulli;
typedef vector<int> vint;

vint _prev;
char *vis, *ans;

void ds(vint *v, int k, int last);


int main(){

    int n, m, t1, t2, cnt;
    cin >> n >> m;
    vint *nar = new vint[n];
    vint *v = new vint[m];

    _prev.resize(m);
    vis = new char[m];
    ans = new char[m];
    for (int i = 0; i < m; i++)
        vis[i] = ans[i] = 0;
    cnt = 0;

    for (int i = 0; i < m; i++){
        cin >> t1 >> t2;
        --t1, --t2;
        nar[t1].push_back(cnt);
        nar[t2].push_back(cnt);
        cnt++;
    }
    for (int i = 0; i < n; i++)
        for (int j = 0; j < nar[i].size(); j++)
            for (int k = 0; k < nar[i].size(); k++)
                if (k != j)
                    v[nar[i][j]].push_back(nar[i][k]);

    cnt = m;

    ds(v, 0, -1);

    for (int i = 0; i < m; i++)
        cnt -= ans[i];
    cout << cnt << endl;
    for (int i = 0; i < m; i++){
        if (!ans[i])
            cout << i + 1 << " ";
    }


    delete [] nar;
    delete [] v;
    delete [] vis;
    delete [] ans;

    return 0;
}


void ds(vint *v, int k, int last){
    _prev[k] = last;
    vis[k] = 1;
    int cur;
    for (int i = 0; i < v[k].size(); i++){
        if (v[k][i] == last)
            continue;
        if (vis[v[k][i]]){
            cur = k;
            do{
                ans[cur] = 1;
                cur = _prev[cur];
            } while (cur != v[k][i]);
            ans[cur] = 1;
        } else
            ds(v, v[k][i], k);
    }
    vis[k] = 0;
}