$Tarjan$大法好$qwq$。

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 #define re register
 6 #define rep(i, a, b) for (re int i = a; i <= b; ++i)
 7 #define repd(i, a, b) for (re int i = a; i >= b; --i)
 8 #define maxx(a, b) a = max(a, b);
 9 #define minn(a, b) a = min(a, b);
10
 
 #define LL long long
11 #define inf (1 << 30)
12 
13 inline int read() {
14     int w = 0, f = 1; char c = getchar();
15     while (!isdigit(c)) f = c == ‘-‘ ? -1 : f, c = getchar();
16     while (isdigit(c)) w = (w << 3) + (w << 1) + (c ^ ‘0‘), c = getchar();
17     return w * f;
 
18 }
19 
20 const int maxn = 1e4 + 5, maxm = 1e5 + 5;
21 
22 struct Edge {
23     int u, v, pre;
24 };
25 
26 struct Graph {
27     Edge ed[maxm << 1];
28     int n, m, G[maxn];
29     void init(int n) {
30         this->n = n;
31         m = 0;
32         memset(G, 0, sizeof(G));
 
33     }
34     void add(int u, int v) {
35         ed[++m] = (Edge){u, v, G[u]};
36         G[u] = m;
37     }
38     int dfs_clock, pre[maxn], low[maxn], iscut[maxn];
39     void dfs(int u, int fa) {
40         pre[u] = low[u] = ++dfs_clock;
41         int child = 0;
42         for (register int i = G[u]; i; i = ed[i].pre) {
43             int v = ed[i].v;
44             if (!pre[v]) {
45                 child++;
46                 dfs(v, u);
47                 minn(low[u], low[v]);
48                 if (low[v] >= pre[u])
49                     iscut[u] = 1;
50             }
51             else if (v != fa) minn(low[u], pre[v]);
52         }
53         if (u == fa && child == 1) iscut[u] = 0;
54     }
55     void tarjan() {
56         memset(pre, 0, sizeof(pre));
57         memset(low, 0, sizeof(low));
58         memset(iscut, 0, sizeof(iscut));
59         dfs_clock = 0;
60         rep(i, 1, n)
61             if (!pre[i])
62                 dfs(i, i);
63         int cnt = 0;
64         rep(i, 1, n)
65             if (iscut[i])
66                 cnt++;
67         printf("%d\n", cnt);
68         rep(i, 1, n)
69             if (iscut[i])
70                 printf("%d ", i);
71     }
72 } G;
73 
74 int n, m;
75 
76 int main() {
77     n = read(), m = read();
78     G.init(n);
79     rep(i, 1, m) {
80         int u = read(), v = read();
81         G.add(u, v), G.add(v, u);
82     }
83     G.tarjan();
84     return 0;
85 }

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