func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long maxn = 5e5 + 50;   const long long mod = 1e9 + 7;   const long long base = maxn * 2;   long long low[maxn];   long long id[maxn];   long long cnt = 0;   long long cntnw = 0;   vector<long long> gr[maxn];   long long par[maxn];   pair<long long, long long> a[maxn];   vector<long long> adj[maxn];   bool dd[maxn];   long long sl[maxn];   stack<long long> st;   vector<long long> adj1[maxn];   long long anc[maxn][22];   long long n, m;   long long siz[maxn];   void dfs(long long u, long long par1) {     dd[u] = 1;     low[u] = id[u] = cnt++;     st.push(u);     for (auto to : adj[u]) {       long long x = a[to].first;       long long y = a[to].second;       long long nxt = x + y - u;       if (nxt == par1) continue;       if (dd[nxt]) {         low[u] = min(low[u], id[nxt]);       } else {         dfs(nxt, u);         low[u] = min(low[u], low[nxt]);         if (low[nxt] >= id[u]) {           cntnw++;           adj1[u].push_back(cntnw);           siz[cntnw] = 1;           vector<long long> vt;           while (1) {             long long p1 = st.top();             st.pop();             adj1[cntnw].push_back(p1);             siz[cntnw]++;             if (p1 == nxt) break;           }         }       }     }   }   vector<long long> topo;   bool kt[maxn];   void dfs1(long long u) {     kt[u] = 1;     for (auto to : adj1[u]) {       if (kt[to]) continue;       dfs1(to);     }     topo.push_back(u);   }   long long dep[maxn];   void dfs2(long long u, long long par) {     anc[u][0] = par;     kt[u] = 1;     for (int i = 1; i < 20; i++) {       anc[u][i] = anc[anc[u][i - 1]][i - 1];     }     for (auto to : adj1[u]) {       if (kt[to]) continue;       dep[to] = dep[u] + 1;       dfs2(to, u);     }   }   long long lca(long long x, long long y) {     if (dep[x] < dep[y]) swap(x, y);     long long kc = dep[x] - dep[y];     for (int i = 20; i >= 0; i--) {       if (kc & (1ll << i)) {         x = anc[x][i];       }     }     if (x == y) return x;     for (int i = 20; i >= 0; i--) {       if (anc[x][i] != anc[y][i]) {         x = anc[x][i];         y = anc[y][i];       }     }     return anc[x][0];   }   long long lca1(long long x, long long y) {     if (dep[x] < dep[y]) swap(x, y);     long long kc = dep[x] - dep[y] - 1;     for (int i = 20; i >= 0; i--) {       if (kc & (1ll << i)) {         x = anc[x][i];       }     }     return x;   }   vector<long long> e[maxn];   int main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     if (fopen( t.inp ,  r )) {       freopen( test.inp ,  r , stdin);       freopen( test.out ,  w , stdout);     }     cin >> n >> m;     for (int i = 1; i <= m; i++) {       cin >> a[i].first >> a[i].second;       adj[a[i].first].push_back(i);       adj[a[i].second].push_back(i);     }     cntnw = n;     for (int i = 1; i <= n; i++) {       if (!dd[i]) {         dfs(i, -1);       }     }     for (int i = 1; i <= n; i++) {       if (!kt[i]) {         dfs1(i);       }     }     reverse(topo.begin(), topo.end());     memset(kt, 0, sizeof(kt));     for (auto to : topo) {       if (kt[to]) continue;       dfs2(to, 0);     }     for (int i = 1; i <= m; i++) {       if (dep[a[i].first] < dep[a[i].second]) swap(a[i].first, a[i].second);       long long l = lca(a[i].first, a[i].second);       if (l == a[i].second) {         e[lca1(a[i].first, a[i].second)].push_back(i);       } else {         e[l].push_back(i);       }     }     vector<long long> ans;     for (int i = n + 1; i <= cntnw; i++) {       if (siz[i] == e[i].size()) {         for (auto to : e[i]) {           ans.push_back(to);         }       }     }     sort(ans.begin(), ans.end());     cout << ans.size() << endl;     for (auto to : ans) {       cout << to <<    ;     }   }   