| /** |
| * Copyright 2016, Quickstep Research Group, Computer Sciences Department, |
| * University of Wisconsin—Madison. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| **/ |
| |
| #ifndef QUICKSTEP_TRANSACTION_STRONGLY_CONNECTED_COMPONENTS_HPP_ |
| #define QUICKSTEP_TRANSACTION_STRONGLY_CONNECTED_COMPONENTS_HPP_ |
| |
| #include <cstddef> |
| #include <cstdint> |
| #include <stack> |
| #include <unordered_map> |
| #include <vector> |
| |
| #include "transaction/DirectedGraph.hpp" |
| #include "utility/Macros.hpp" |
| |
| namespace quickstep { |
| namespace transaction { |
| |
| /** \addtogroup Transaction |
| * @{ |
| */ |
| |
| /** |
| * @brief Class for applying Tarjan's strongly connected components algorithm |
| * to a directed graph. The class finds and stores information to |
| * identify components and nodes-to-component mapping. For all nodes |
| * v, w in a strongly connected component, there is a path from v to w, |
| * and a path from w to v. |
| **/ |
| class StronglyConnectedComponents { |
| public: |
| /** |
| * @brief Constructor. |
| * |
| * @param directed_graph The directed graph which the algorithm runs. |
| **/ |
| explicit StronglyConnectedComponents(const DirectedGraph &directed_graph); |
| |
| /** |
| * @brief Getter for the component id of the node. |
| * |
| * @param node_id Id of the node in the graph. |
| * @return Id of the component to which the given node belongs. |
| **/ |
| inline std::uint64_t getComponentId(DirectedGraph::node_id node_id) const { |
| return component_ids_[node_id]; |
| } |
| |
| /** |
| * @brief Getter for total number of strongly connected components. |
| * @warning This method should be called after findStronglyConnectedComponents(). |
| * |
| * @return Total number of strongly connected components. |
| **/ |
| inline std::size_t getTotalComponents() const { |
| return no_of_components_; |
| } |
| |
| /** |
| * @brief Gets a component id to list of node ids mapping. |
| * |
| * @return Mapping of component ids to list of nodes. |
| **/ |
| std::unordered_map<std::uint64_t, std::vector<DirectedGraph::node_id>> getComponentMapping() const; |
| |
| private: |
| // Enumarates all strongly connected components, and stores node-to-component |
| // mapping in the graph. |
| void findStronglyConnectedComponents(); |
| |
| // Applies DFS to the node whic has id v. |
| void depthFirstSearch(DirectedGraph::node_id v); |
| |
| // Const reference to the graph. |
| const DirectedGraph &directed_graph_; |
| |
| // is_marked[v] == true if depth first search traversed the node with id v. |
| std::vector<bool> is_marked_; |
| |
| // component_ids_[v] == i if strongly connected component |
| // which the node with id v belongs to, has id i. |
| std::vector<std::uint64_t> component_ids_; |
| |
| // low_ids_[v] == i if lowest traversal id seen by the node |
| // with id v equals i. |
| std::vector<std::uint64_t> low_ids_; |
| |
| // Keeps track of the nodes in the current traversal of the graph. |
| std::stack<DirectedGraph::node_id> traversal_stack_; |
| |
| // Keeps track of the current index number of depth first search traversal. |
| std::uint64_t preorder_counter_; |
| |
| // Keeps track of the current number of the strongly connected component. |
| std::uint64_t no_of_components_; |
| |
| DISALLOW_COPY_AND_ASSIGN(StronglyConnectedComponents); |
| }; |
| |
| /** @} */ |
| |
| } // namespace transaction |
| } // namespace quickstep |
| |
| #endif // QUICKSTEP_TRANSACTION_STRONGLY_CONNECTED_COMPONENTS_HPP_ |