P8435 【模板】点双连通分量

https://www.luogu.com.cn/record/130733145

Luogu/P8435/P8435.cpp

@@ -0,0 +1,95 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#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;
+int idx, head[N], ver[M << 1], next[M << 1];
+int cnt, dcc_cnt, dfn[N], low[N];
+std::stack<int> st;
+bool cut[N];
+std::vector<int> dcc_points[N];
+
+void add(int u, int v) {
+    next[idx] = head[u];
+    ver[idx] = v;
+    head[u] = idx++;
+}
+
+void tarjan(int u, int root) {
+    dfn[u] = low[u] = ++cnt;
+    st.emplace(u);
+
+    if (u == root && head[u] == -1) {
+        dcc_points[++dcc_cnt].emplace_back(u);
+
+        return;
+    }
+
+    for (int i = head[u]; ~i; i = next[i]) {
+        int v = ver[i];
+
+        if (!dfn[v]) {
+            tarjan(v, root);
+            low[u] = std::min(low[u], low[v]);
+
+            if (dfn[u] <= low[v]) {
+                dcc_cnt++;
+
+                int vv;
+
+                do {
+                    vv = st.top();
+                    st.pop();
+                    dcc_points[dcc_cnt].emplace_back(vv);
+                } while (vv != v);
+
+                dcc_points[dcc_cnt].emplace_back(u);
+            }
+        } else {
+            low[u] = std::min(low[u], dfn[v]);
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    std::fill(std::begin(head), std::end(head), -1);
+
+    cin >> n >> m;
+
+    for (int i = 1, u, v; i <= m; i++) {
+        cin >> u >> v;
+
+        if (u == v) continue;
+
+        add(u, v);
+        add(v, u);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (!dfn[i]) tarjan(i, i);
+    }
+
+    cout << dcc_cnt << endl;
+
+    for (int i = 1; i <= dcc_cnt; i++) {
+        cout << dcc_points[i].size() << ' ';
+
+        std::copy(std::begin(dcc_points[i]), std::end(dcc_points[i]), std::ostream_iterator<int>(cout, " "));
+
+        cout << endl;
+    }
+
+    return 0;
+}