P7687 [CEOI2005] Critical Network Lines

https://www.luogu.com.cn/record/102265524

Luogu/P7687/P7687.cpp

@@ -0,0 +1,76 @@
+#include <iostream>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, m, k, l, a[N], b[N];
+std::vector<int> g[N];
+int dfn[N], low[N];
+bool bridge[N];
+std::vector<std::pair<int, int>> ans;
+
+void tarjan(int u, int f) {
+    static int cnt = 0;
+
+    dfn[u] = low[u] = ++cnt;
+
+    for (int v : g[u]) {
+        if (!dfn[v]) {
+            tarjan(v, u);
+
+            low[u] = std::min(low[u], low[v]);
+
+            if (dfn[u] < low[v]) {
+                if (a[v] == 0 || b[v] == 0 || a[v] == k || b[v] == l) {
+                    ans.emplace_back(u, v);
+                }
+            }
+
+            a[u] += a[v];
+            b[u] += b[v];
+        } else if (v != f) {
+            low[u] = std::min(low[u], dfn[v]);
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m >> k >> l;
+
+    for (int i = 1, x; i <= k; i++) {
+        cin >> x;
+
+        a[x] = 1;
+    }
+
+    for (int i = 1, x; i <= l; i++) {
+        cin >> x;
+
+        b[x] = 1;
+    }
+
+    for (int i = 1, u, v; i <= m; i++) {
+        cin >> u >> v;
+
+        g[u].push_back(v);
+        g[v].push_back(u);
+    }
+
+    tarjan(1, 1);
+
+    cout << ans.size() << endl;
+
+    for (auto e : ans) {
+        cout << e.first << ' ' << e.second << endl;
+    }
+
+    return 0;
+}