refactor: better e_bcc

src/code/graph/e_bcc.hpp

@@ -1,45 +1,36 @@
 #ifndef TIFALIBS_GRAPH_E_BCC
 #define TIFALIBS_GRAPH_E_BCC
 
-#include "../util/util.hpp"
+#include "eog.hpp"
 
 namespace tifa_libs::graph {
 
-template <class EW>
-class e_bcc {
-  vvec<EW> CR g;
-
- public:
-  u32 id;
-  vecu ebcc_id, dfn, low;
-  vecb cut;
+struct e_bcc {
+  vecu dfn, low;
   vvecu belongs;
 
-  //! EW need rev_edge
-  CEXPE e_bcc(vvec<EW> CR G) NE : g(G) { build(); }
-
-  CEXP void build() NE {
-    u32 cnt = 0, n = u32(g.size());
-    id = 0, dfn = low = ebcc_id = vecu(n, n), cut = vecb(n, 0);
-    vecu s;
-    auto f = [&](auto &&f, u32 u, u32 fa, u32 inv_from) NE -> void {
-      dfn[u] = low[u] = cnt++, s.push_back(u);
-      flt_ (u32, i, 0, (u32)g[u].size()) {
-        auto v = g[u][i];
-        if (v.to == fa && i == inv_from) continue;
-        if (dfn[v.to] == n) f(f, v.to, u, v.inv), low[u] = min(low[u], low[v.to]);
-        else low[u] = min(low[u], dfn[v.to]);
-      }
+  //! g should be undirect
+  template <bool with_deg>
+  CEXP e_bcc(eog<with_deg> CR g) NE : dfn(g.v_cnt()), low(g.v_cnt()) {
+    vecu stk;
+    u32 tot = 0;
+    auto tarjan = [&](auto&& f, u32 u, u32 fa_eid) -> void {
+      dfn[u] = low[u] = ++tot;
+      stk.push_back(u);
+      g.foreach(u, [&](u32 eid, u32 v, u32) {
+        if (!dfn[v]) f(f, v, eid), low[u] = min(low[u], low[v]);
+        else if (eid != fa_eid && eid != (fa_eid ^ 1)) low[u] = min(low[u], dfn[v]);
+      });
       if (low[u] == dfn[u]) {
-        belongs.push_back(vecu());
-        do {
-          const u32 v = s.back();
-          if (s.pop_back(), ebcc_id[v] = id, belongs[id].push_back(v); v == u) return void(++id);
-        } while (1);
+        vecu res;
+        u32 p;
+        do res.push_back(p = stk.back()), stk.pop_back();
+        while (u != p);
+        belongs.emplace_back(std::move(res));
       }
     };
-    flt_ (u32, i, 0, n)
-      if (dfn[i] == n) f(f, i, i, -1_u32);
+    flt_ (u32, i, 0, g.v_cnt())
+      if (!dfn[i]) tarjan(tarjan, i, -1_u32);
   }
 };
 

src/code/graph/eog.hpp

@@ -15,14 +15,22 @@ struct eog {
   CEXPE eog(u32 n = 0) NE : head(n, -1_u32), e(), cnt_arc{0}, deg_in(0), deg_out(0) {
     if CEXP (with_deg) deg_in.resize(n), deg_out.resize(n);
   }
+  CEXP u32 v_cnt() CNE { return (u32)head.size(); }
+  CEXP u32 arc_cnt() CNE { return (u32)e.size(); }
   CEXP void add_arc(u32 u, u32 v) NE {
     e.emplace_back(v, head[u]), head[u] = u32(e.size() - 1);
     if CEXP (++cnt_arc; with_deg) ++deg_in[v], ++deg_out[u];
   }
+  CEXP void add_edge(u32 u, u32 v) NE { add_arc(u, v), add_arc(v, u); }
   CEXP void pop_startwith(u32 now) NE {
     if CEXP (--cnt_arc; with_deg) --deg_in[e[head[now]].first], --deg_out[now];
     head[now] = e[head[now]].second;
   }
+  template <class F>
+  requires requires(F f, u32 eid, u32 to, u32 next) { f(eid, to, next); }
+  CEXP void foreach(u32 u, F&& f) CNE {
+    for (u32 i = head[u]; ~i; i = e[i].second) f(i, e[i].first, e[i].second);
+  }
 };
 template <class T, bool with_deg = false>
 struct eogw {

src/code/graph/v_bcc.hpp

@@ -11,7 +11,7 @@ struct v_bcc {
   vvecu belongs;
   vecb cut;
 
-  //! G should be undirect
+  //! g should be undirect
   template <bool with_deg>
   CEXP v_bcc(alist<with_deg> CR g) NE : dfn(g.size()), low(g.size()) {
     if CEXP (get_cut) cut = vecb(g.size());

src/test_cpverifier/library-checker-graph/two_edge_connected_components.test.cpp

@@ -0,0 +1,22 @@
+#define PROBLEM "https://judge.yosupo.jp/problem/two_edge_connected_components"
+
+#include "../../code/graph/e_bcc.hpp"
+
+int main() {
+  std::cin.tie(nullptr)->std::ios::sync_with_stdio(false);
+  u32 n, m;
+  std::cin >> n >> m;
+  tifa_libs::graph::eog g(n);
+  for (u32 i = 0, u, v; i < m; ++i) {
+    std::cin >> u >> v;
+    g.add_edge(u, v);
+  }
+  tifa_libs::graph::e_bcc bcc(g);
+  std::cout << bcc.belongs.size() << '\n';
+  for (auto&& b : bcc.belongs) {
+    for (std::cout << b.size(); auto x : b)
+      std::cout << ' ' << x;
+    std::cout << '\n';
+  }
+  return 0;
+}

src/test_tinplate/graph/e_bcc.cpp

@@ -6,20 +6,16 @@ int main() {
   std::cin.tie(nullptr)->std::ios::sync_with_stdio(false);
   u32 n, m;
   std::cin >> n >> m;
-  struct EW {
-    u32 to, inv;
-  };
-  vvec<EW> e(n);
+  tifa_libs::graph::eog g(n);
   for (u32 i = 0, u, v; i < m; ++i) {
-    std::cin >> u >> v, --u, --v;
-    if (u == v) continue;
-    u32 tem1 = u32(e[u].size()), tem2 = u32(e[v].size());
-    e[u].push_back({v, tem2}), e[v].push_back({u, tem1});
+    std::cin >> u >> v;
+    --u, --v;
+    g.add_edge(u, v);
   }
-  tifa_libs::graph::e_bcc<EW> bcc(e);
-  std::cout << bcc.id << '\n';
-  for (u32 i = 0; i < bcc.id; ++i) {
-    for (std::cout << bcc.belongs[i].size() << ' '; auto x : bcc.belongs[i])
+  tifa_libs::graph::e_bcc bcc(g);
+  std::cout << bcc.belongs.size() << '\n';
+  for (auto&& b : bcc.belongs) {
+    for (std::cout << b.size() << ' '; auto x : b)
       std::cout << x + 1 << ' ';
     std::cout << '\n';
   }