1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 const int maxn = 1e5 + 5, maxm = 5e5 + 5;
 6 
 7 int N, M;
 8 
 9 struct Edge {
10     int u, v, pre;
11 } e[maxm];
12 int m, G[maxn];
13 
14 void init() {
15     memset(G, -1, sizeof(G));
16     m = 0;
17 }
18 void add(int u, int v) {
19     e[m++] = (Edge){u, v, G[u]};
20     G[u] = m-1;
21 }
22 
23 stack<pair<int, int> > s;
24 vector<int> bcc[maxn];
25 int bcc_cnt, bccno[maxn];
26 int cut[maxn], pre[maxn], low[maxn], dfs_clock;
27 
28 void dfs(int u, int fa) {
29     low[u] = pre[u] = ++dfs_clock;
30     int child = 0;
31     for (register int i = G[u]; ~i; i = e[i].pre) {
32         int v = e[i].v;
33         if (!pre[v]) {
34             child++;
35             s.push(make_pair(u, v));
36             dfs(v, u);
37             if (low[v] >= pre[u]) {
38                 cut[u] = 1;
39                 bcc_cnt++; // 找到一个双连通分量
40                 for (;;) {
41                     pair<int, int> e = s.top(); s.pop();
42                     if (bccno[e.first] != bcc_cnt) bccno[e.first] = bcc_cnt, bcc[bcc_cnt].push_back(e.first);
43                     if (bccno[e.second] != bcc_cnt) bccno[e.second] = bcc_cnt, bcc[bcc_cnt].push_back(e.second);
44                     if (e.first == u) break;
45                 }
46             }
47             low[u] = min(low[u], low[v]);
48         } else
49             if (v != fa) low[u] = min(low[u], pre[v]);
50     }
51     if (u == fa && child == 1) cut[u] = 0;
52 }
53 
54 void work() {
55     memset(pre, 0, sizeof(pre));
56     memset(cut, 0, sizeof(cut));
57     bcc_cnt = dfs_clock = 0;
58     for (register int i = 1; i <= N; i++)
59         if (!pre[i])
60             dfs(i, i);
61     // 输出
62     printf("BCC : %d\n", bcc_cnt);
63     for (register int i = 1; i <= bcc_cnt; i++) {
64         printf("[%d]", i);
65         for (register int j = 0; j < bcc[i].size(); j++)
66             printf(" %d", bcc[i][j]);
67         printf("\n");
68     }
69 }
70 
71 int main() {
72     scanf("%d%d", &N, &M);
73     init();
74     for (register int i = 1; i <= M; i++) {
75         int u, v;
76         scanf("%d%d", &u, &v);
77         add(u, v); add(v, u);
78     }
79     work();
80     return 0;
81 }