convert this now

Author: lrvideckis

library/graphs/bridges_cuts/block_vertex_tree.hpp

@@ -19,14 +19,14 @@
 //! @time O(n + m)
 //! @time O(n)
 template<class G>
-vector<vi> block_vertex_tree(const G& adj,
-  const cuts<G>& cc) {
+vector<vi> block_vertex_tree(const G& adj, int num_bccs,
+  const vi& bcc_id) {
   int n = sz(adj);
-  vector<vi> bvt(n + cc.num_bccs);
-  vector<bool> vis(cc.num_bccs);
+  vector<vi> bvt(n + num_bccs);
+  vector<bool> vis(num_bccs);
   rep(i, 0, n) {
     for (auto [_, e_id] : adj[i]) {
-      int bccid = cc.bcc_id[e_id];
+      int bccid = bcc_id[e_id];
       if (!vis[bccid]) {
         vis[bccid] = 1;
         bvt[i].push_back(bccid + n);

library/graphs/bridges_cuts/cuts.hpp

@@ -18,39 +18,35 @@
 //! bcc_id[edge id] = id, 0<=id<num_bccs
 //! @time O(n + m)
 //! @space O(n + m)
-template<class G> struct cuts {
-  int num_bccs = 0;
-  vector<bool> is_cut;
-  vi bcc_id;
-  cuts(const G& adj, int m):
-    is_cut(sz(adj)), bcc_id(m, -1) {
-    int n = sz(adj), timer = 1;
-    vi tin(n), st;
-    auto dfs = [&](auto&& self, int v, int p_id) -> int {
-      int low = tin[v] = timer++, deg = 0;
-      for (auto [u, e_id] : adj[v]) {
-        assert(v != u);
-        if (e_id == p_id) continue;
-        if (!tin[u]) {
-          int siz = sz(st);
-          st.push_back(e_id);
-          int low_ch = self(self, u, e_id);
-          if (low_ch >= tin[v]) {
-            is_cut[v] = 1;
-            rep(i, siz, sz(st)) bcc_id[st[i]] = num_bccs;
-            st.resize(siz);
-            num_bccs++;
-          }
-          low = min(low, low_ch);
-          deg++;
-        } else if (tin[u] < tin[v]) {
-          st.push_back(e_id);
-          low = min(low, tin[u]);
+template<class G>
+tuple<int, vi, vi> cuts(const G& adj, int m) {
+  int n = sz(adj), num_bccs = 0, timer = 0;
+  vi bcc_id(m, -1), is_cut(n), tin(n), st;
+  auto dfs = [&](auto&& self, int v, int p_id) -> int {
+    int low = tin[v] = ++timer, deg = 0;
+    for (auto [u, e_id] : adj[v]) {
+      assert(v != u);
+      if (e_id == p_id) continue;
+      if (!tin[u]) {
+        int siz = sz(st);
+        st.push_back(e_id);
+        int low_ch = self(self, u, e_id);
+        if (low_ch >= tin[v]) {
+          is_cut[v] = 1;
+          rep(i, siz, sz(st)) bcc_id[st[i]] = num_bccs;
+          st.resize(siz);
+          num_bccs++;
         }
+        low = min(low, low_ch);
+        deg++;
+      } else if (tin[u] < tin[v]) {
+        st.push_back(e_id);
+        low = min(low, tin[u]);
       }
-      if (p_id == -1) is_cut[v] = (deg > 1);
-      return low;
-    };
-    rep(i, 0, n) if (!tin[i]) dfs(dfs, i, -1);
-  }
-};
+    }
+    if (p_id == -1) is_cut[v] = (deg > 1);
+    return low;
+  };
+  rep(i, 0, n) if (!tin[i]) dfs(dfs, i, -1);
+  return {num_bccs, bcc_id, is_cut};
+}

tests/library_checker_aizu_tests/graphs/biconnected_components.test.cpp

@@ -15,34 +15,35 @@ int main() {
     adj[v].emplace_back(u, i);
     edges[i] = make_pair(u, v);
   }
-  cuts cc(adj, m);
-  vector<vector<int>> bvt = block_vertex_tree(adj, cc);
-  assert(find(begin(cc.bcc_id), end(cc.bcc_id), -1) ==
-    end(cc.bcc_id));
+  auto [num_bccs, bcc_id, is_cut] = cuts(adj, m);
+  vector<vector<int>> bvt =
+    block_vertex_tree(adj, num_bccs, bcc_id);
+  assert(
+    find(begin(bcc_id), end(bcc_id), -1) == end(bcc_id));
   for (int i = 0; i < n; i++) {
     // cut node if there exists a pair of adjacent edges
     // belonging to different BCCs
-    bool is_cut = 0;
+    bool curr_is_cut = 0;
     for (int j = 0; j < sz(adj[i]); j++)
-      if (cc.bcc_id[adj[i][0].second] !=
-        cc.bcc_id[adj[i][j].second])
-        is_cut = 1;
-    assert(is_cut == cc.is_cut[i]);
+      if (bcc_id[adj[i][0].second] !=
+        bcc_id[adj[i][j].second])
+        curr_is_cut = 1;
+    assert(curr_is_cut == is_cut[i]);
   }
   // check correctness of block vertex tree
   for (int i = 0; i < n; i++) {
     assert(sz(adj[i]) >=
       sz(bvt[i])); // in particular, if empty(adj[i]), then
                    // empty(bct[i])
-    assert(cc.is_cut[i] ==
+    assert(is_cut[i] ==
       (sz(bvt[i]) >
         1)); // is cut means non-leaf in block vertex tree
   }
   {
-    vector<set<int>> bcc_to_nodes(cc.num_bccs),
+    vector<set<int>> bcc_to_nodes(num_bccs),
       node_to_bccs(n);
     for (int i = 0; i < m; i++) {
-      int bccid = cc.bcc_id[i];
+      int bccid = bcc_id[i];
       for (auto node : {edges[i].first, edges[i].second}) {
         bcc_to_nodes[bccid].insert(node);
         node_to_bccs[node].insert(bccid);
@@ -56,7 +57,7 @@ int main() {
         assert(node_to_bccs[u].contains(bccid));
       }
     }
-    for (int bccid = 0; bccid < cc.num_bccs; bccid++) {
+    for (int bccid = 0; bccid < num_bccs; bccid++) {
       assert(
         sz(bcc_to_nodes[bccid]) == sz(bvt[bccid + n]));
       for (auto u : bvt[bccid + n])
@@ -66,8 +67,8 @@ int main() {
   vector<int> lone_nodes;
   for (int u = 0; u < n; u++)
     if (empty(bvt[u])) lone_nodes.push_back(u);
-  cout << cc.num_bccs + sz(lone_nodes) << '\n';
-  for (int bccid = 0; bccid < cc.num_bccs; bccid++) {
+  cout << num_bccs + sz(lone_nodes) << '\n';
+  for (int bccid = 0; bccid < num_bccs; bccid++) {
     cout << sz(bvt[bccid + n]) << " ";
     for (auto u : bvt[bccid + n]) cout << u << " ";
     cout << '\n';