Add edge removal method and tree repair, TODO: handle Eext

algorithm/frigioni.h

@@ -17,26 +17,26 @@ public:
 
   Frigioni(Digraph<T> G) { this->G = G; }
 
-  //
+  // Initialize the decremental maintenance data structure for general graphs
   void init() override;
 
-  //
+  // Execute reachability query q(u, v) from vertex u to vertex v
+  // in O(1) using the transitive closure matrix
   bool query(const T& u, const T& v) override;
 
-  //
+  // Delete edge e(u, v)
   void remove(const T& u, const T& v) override;
+
+  // Delete set of edges and explicitely maintain the transitive closure
+  void remove(const std::vector<std::pair<T, T>>& edges);
 private:
   // Transitive closure matrix, used to answer reachability queries in O(1)
   std::map<T, std::map<T, bool>> TC;
 
-  // Connect each vertex with its representative SCC
-  std::map<T, SCC<T>> C;
-
-  // Each scc's representative vertex reachability tree
+  // For each SCC, store a reachability tree created as a BFS tree
   std::map<T, BreadthFirstTree<T>> RT;
 
-  // Incoming / Outgoing / Internal edges of each SCC
-  // Maps each SCC representative with struct Edges
+  // For each SCC, store collections of incoming, outgoing and internal edges
   struct Edges {
     std::set<std::pair<T, T>> in;
     std::set<std::pair<T, T>> inc;
@@ -45,20 +45,19 @@ private:
   std::map<T, Edges> E;
   
   // Decremental maintenance of strongly connected components
-  RodittyZwick<T> decremental;
+  RodittyZwick<T> rodittyZwick;
 };
 
 template<typename T>
 void Frigioni<T>::init() {
   auto SCCs = Tarjan<T>(this->G.adjMatrix).execute();
-  decremental = RodittyZwick<T>(this->G);
-  decremental.init();
+  rodittyZwick = RodittyZwick<T>(this->G);
+  rodittyZwick.init();
 
   for (auto& scc : SCCs) {
     RT[scc.id] = BreadthFirstTree<T>(this->G, scc.id);
     for (const auto& u : this->G.vertices()) {
       for (const auto& v : this->G.adjMatrix[u]) {
-        TC[u][v] = false;
         if (scc.member(u)) {
           if (scc.member(v))
             E[scc.id].in.insert(std::make_pair(u, v));  
@@ -67,18 +66,17 @@ void Frigioni<T>::init() {
         } else if (scc.member(v)) {
           E[scc.id].inc.insert(std::make_pair(u, v));
         }
+        TC[u][v] = false;
       }
     }
   }
   for (auto& scc : SCCs) {
-    for (const auto& u : this->G.vertices()) {
-      if (scc.member(u)) {
+    for (const auto& u : scc.vertices()) {
       for (const auto& v : RT[scc.id].vertices()) {
         TC[u][v] = true;
       }
     }
   }
-  }
 }
 
 template<typename T>
@@ -91,6 +89,84 @@ void Frigioni<T>::remove(const T& u, const T& v) {
   
 }
 
+template<typename T>
+void Frigioni<T>::remove(const std::vector<std::pair<T, T>>& edges) {
+  std::vector<std::pair<T, T>> Eint;
+  std::vector<std::pair<T, T>> Eext;
+
+  // Put incoming edge removal requests in the corresponding collection
+  for (const auto& [u, v] : edges) {
+    if (rodittyZwick.query(u, v))
+      Eint.push_back({ u, v });
+    else
+      Eext.push_back({ u, v });
+  }
+
+  std::map<T, std::stack<T>> H;
+
+  // Handle SCC internal edge removals
+  for (const auto& [u, v] : Eint) {
+    this->G.remove(u, v);
+    rodittyZwick.remove(u, v);
+
+    if (!rodittyZwick.query(u, v)) {
+      auto C = rodittyZwick.getSCCs();
+      auto D = E[u]; // or E[v], the component that's been split
+      E.erase(u);
+
+      for (const auto& [w, z] : D.inc) {
+        E[C[z].id].inc.insert({ w, z });
+        // check if scc needs hook
+      }
+
+      for (const auto& [w, z] : D.out) {
+        E[C[z].id].out.insert({ w, z });
+        // check if scc needs hook
+      }
+
+      for (const auto& [w, z] : D.in) {
+        if (C[w] == C[z])
+          E[C[w].id].in.insert({ w, z });
+        else {
+          E[C[w].id].out.insert({ w, z });
+          E[C[z].id].in.insert({ w, z });
+        }
+      }
+    } else {
+      E[u].in.erase({ u, v });
+    }
+  }
+
+  // Handle SCC external edge removals
+  for (const auto& [u, v] : Eext) {
+    this->G.remove(u, v);
+    // TODO
+  }
+
+  // Repair the trees
+  for (const auto& id : std::views::keys(rodittyZwick.getSCCs())) {
+    while (H[id].size() > 0) {
+      const auto& h = H[id].top();
+      bool found = false;
+      
+      for (const auto& [u, v] : E[h].inc) {
+        if (RT[id].contains(id, u)) {
+          RT[id].adjMatrix[u].insert(h);
+          found = true;
+          break;
+        }
+      }
+      H[id].pop();
+      if (!found) {
+        TC[id][h] = false;
+        for (const auto& [u, v] : E[h].out) {
+          H[id].push(v);
+        }
+      }
+    }
+  }
+}
+
 } // namespace algo
 
 #endif