func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxn = 100010;   int n, m;   int low[maxn], dfn[maxn], v[maxn << 1], A[maxn];   int nxt[maxn << 1], head[maxn], belong[maxn], a[maxn], vis[maxn << 1];   stack<int> s;   int indexs = 0, cnt = 0;   int ans = 0;   void add_edge(int x, int y) {     static int N = 1;     N++;     v[N] = y;     nxt[N] = head[x];     head[x] = N;   }   void tarjan(int x, int fa) {     dfn[x] = low[x] = ++indexs;     for (int i = head[x]; i != -1; i = nxt[i]) {       if (vis[i]) continue;       vis[i] = vis[i ^ 1] = 1;       s.push(i);       if (!dfn[v[i]]) {         tarjan(v[i], x);         low[x] = min(low[x], low[v[i]]);         if (low[v[i]] >= dfn[x]) {           cnt++;           int num = 0, bcnt = 0;           while (1) {             int tmp = s.top();             s.pop();             if (belong[v[tmp]] != cnt) belong[v[tmp]] = cnt, num++;             if (belong[v[tmp ^ 1]] != cnt) belong[v[tmp ^ 1]] = cnt, num++;             a[++bcnt] = tmp;             if (tmp == i) break;           }           if (num == bcnt)             for (int i = 1; i <= bcnt; i++) A[++ans] = a[i];         }       } else         low[x] = min(low[x], dfn[v[i]]);     }   }   int main() {     memset(head, -1, sizeof(head));     scanf( %d%d , &n, &m);     for (int i = 1; i <= m; i++) {       int x, y;       scanf( %d%d , &x, &y);       add_edge(x, y);       add_edge(y, x);     }     for (int i = 1; i <= n; i++)       if (!dfn[i]) tarjan(i, 0);     sort(A + 1, A + 1 + ans);     printf( %d n , ans);     for (int i = 1; i <= ans; i++) cout << (A[i] >> 1) <<    ;     return 0;   }   