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80 lines
2.1 KiB
80 lines
2.1 KiB
/* Distributed under the OSI-approved BSD 3-Clause License. See accompanying
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file Copyright.txt or https://cmake.org/licensing for details. */
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#ifndef cmComputeComponentGraph_h
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#define cmComputeComponentGraph_h
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#include "cmConfigure.h" // IWYU pragma: keep
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#include <stack>
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#include <vector>
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#include "cmGraphAdjacencyList.h"
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/** \class cmComputeComponentGraph
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* \brief Analyze a graph to determine strongly connected components.
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*
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* Convert a directed graph into a directed acyclic graph whose nodes
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* correspond to strongly connected components of the original graph.
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*
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* We use Tarjan's algorithm to enumerate the components efficiently.
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* An advantage of this approach is that the components are identified
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* in a topologically sorted order.
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*/
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class cmComputeComponentGraph
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{
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public:
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// Represent the graph with an adjacency list.
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using NodeList = cmGraphNodeList;
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using EdgeList = cmGraphEdgeList;
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using Graph = cmGraphAdjacencyList;
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cmComputeComponentGraph(Graph const& input);
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~cmComputeComponentGraph();
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/** Get the adjacency list of the component graph. */
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Graph const& GetComponentGraph() const { return this->ComponentGraph; }
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EdgeList const& GetComponentGraphEdges(int c) const
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{
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return this->ComponentGraph[c];
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}
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/** Get map from component index to original node indices. */
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std::vector<NodeList> const& GetComponents() const
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{
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return this->Components;
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}
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NodeList const& GetComponent(int c) const { return this->Components[c]; }
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/** Get map from original node index to component index. */
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std::vector<int> const& GetComponentMap() const
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{
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return this->TarjanComponents;
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}
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private:
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void TransferEdges();
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Graph const& InputGraph;
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Graph ComponentGraph;
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// Tarjan's algorithm.
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struct TarjanEntry
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{
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int Root;
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int VisitIndex;
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};
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std::vector<int> TarjanVisited;
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std::vector<int> TarjanComponents;
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std::vector<TarjanEntry> TarjanEntries;
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std::vector<NodeList> Components;
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std::stack<int> TarjanStack;
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int TarjanWalkId;
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int TarjanIndex;
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void Tarjan();
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void TarjanVisit(int i);
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// Connected components.
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};
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#endif
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