Rename decrementalscc to rodittyzwick as it is the core algorithm

algorithm/roditty_zwick.h

@@ -0,0 +1,101 @@
+#ifndef RODITTY_ZWICK_H_
+#define RODITTY_ZWICK_H_
+
+#include "algorithm/decremental_reachability.h"
+#include "algorithm/tarjan.h"
+#include "graph/breadth_first_tree.h"
+
+using namespace graph;
+
+namespace algo {
+
+template<typename T>
+class RodittyZwick : public DecrementalReachability<T> {
+public:
+  RodittyZwick() = default;
+
+  RodittyZwick(Digraph<T> G) { this->G = G; }
+
+  //
+  void init() override;
+
+  //
+  void findSCC();
+
+  // Return true if u and v are in the same SCC
+  bool query(const T& u, const T& v) override;
+
+  // Remove edge (u,v) and update A accordingly for fast checking query
+  void remove(const T& u, const T& v) override;
+
+  void setGraph(Digraph<T> G);
+private:
+  // Array used to answer strong connectivity queries in O(1) time
+  std::map<T, T> A;
+
+  // Connect each representative with its SCC
+  std::map<T, SCC<T>> C;
+
+  // Maintain in-out bfs trees
+  std::map<T, BreadthFirstTree<T>> inTree;
+  std::map<T, BreadthFirstTree<T>> outTree;
+};
+
+template<typename T>
+void RodittyZwick<T>::init() {
+  findSCC();
+}
+
+template<typename T>
+void RodittyZwick<T>::findSCC() {
+  auto SCCs = Tarjan<T>(this->G.adjMatrix).execute();
+  
+  for (auto& SCC : SCCs) {
+    const auto& w = SCC.id;
+
+    for (const auto& v : std::views::keys(SCC.adjMatrix))
+      A[v] = w;
+    
+    outTree[w] = BreadthFirstTree<T>(SCC, w);
+    inTree[w] = BreadthFirstTree<T>(SCC.reverse(), w);
+
+    C[w] = SCC;
+  }
+}
+
+template<typename T>
+bool RodittyZwick<T>::query(const T& u, const T& v) {
+  return A[u] == A[v];
+}
+
+template<typename T>
+void RodittyZwick<T>::remove(const T& u, const T& v) {
+  const auto& w = A[u];
+  C[w].remove(u, v);
+  this->G.remove(u, v);
+
+  // If u and v are not in the same SCC, do nothing
+  if (A[u] != A[v]) return;
+
+  // If edge (u,v) is not contained in both inTree and outTree do nothing
+  if (!inTree[w].adjMatrix[u].contains(v) &&
+      !outTree[w].adjMatrix[u].contains(v))
+    return;
+
+  // Update In(w) and Out(w)
+  outTree[w] = BreadthFirstTree<T>(C[w], w);
+  inTree[w] = BreadthFirstTree<T>(C[w].reverse(), w);
+
+  // If a SCC is broken, compute all SCCs again
+  if (!inTree[w].adjMatrix.count(u) || !outTree[w].adjMatrix.count(v))
+    findSCC();
+}
+
+template<typename T>
+void RodittyZwick<T>::setGraph(Digraph<T> G) {
+  this->G = G;
+}
+
+}; // namespace algo
+
+#endif