P8436 【模板】边双连通分量

https://www.luogu.com.cn/record/94754317

Luogu/P8436/P8436.cpp

@@ -0,0 +1,86 @@
+#include <iostream>
+#include <algorithm>
+#include <stack>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5,
+          M = 2e6 + 5;
+
+int n, m, ans;
+int idx, head[N], edge[M << 1], next[M << 1];
+int cnt, dcc_cnt, dfn[N], low[N];
+std::stack<int> st;
+std::vector<int> nodes[N];
+
+void add(int u, int v) {
+    next[idx] = head[u];
+    edge[idx] = v;
+    head[u] = idx++;
+}
+
+void tarjan(int u, int in_edge) {
+    dfn[u] = low[u] = ++cnt;
+    st.push(u);
+
+    for (int i = head[u]; ~i; i = next[i]) {
+        int v = edge[i];
+
+        if (!dfn[v]) {
+            tarjan(v, i);
+            low[u] = std::min(low[u], low[v]);
+        } else if (i != (in_edge ^ 1)) {
+            low[u] = std::min(low[u], dfn[v]);
+        }
+    }
+
+    if (low[u] == dfn[u]) {
+        dcc_cnt++;
+
+        int v;
+        do {
+            v = st.top();
+            st.pop();
+            nodes[dcc_cnt].push_back(v);
+        } while (v != u);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    std::fill_n(head, N, -1);
+
+    cin >> n >> m;
+
+    for (int i = 1, u, v; i <= m; i++) {
+        cin >> u >> v;
+
+        add(u, v);
+        add(v, u);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (!dfn[i]) {
+            tarjan(i, -1);
+        }
+    }
+
+    cout << dcc_cnt << endl;
+
+    for (int i = 1; i <= dcc_cnt; i++) {
+        cout << nodes[i].size() << ' ';
+
+        for (int x : nodes[i]) {
+            cout << x << ' ';
+        }
+
+        cout << endl;
+    }
+
+    return 0;
+}