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include/DataStructures/Graphs/Subgraph.hpp

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+/**
+ * Subgraph.hpp
+ *
+ *  Created on: May 8, 2019
+ *      Author: Franziska Wegner, Matthias Wolf
+ */
+
+#ifndef EGOA__DATA_STRUCTURES__GRAPHS__SUBGRAPH_HPP
+#define EGOA__DATA_STRUCTURES__GRAPHS__SUBGRAPH_HPP
+
+#include <algorithm>
+#include <ostream>
+#include <vector>
+
+#include "DataStructures/Views/VectorView.hpp"
+
+#include "Exceptions/Assertions.hpp"
+
+
+namespace egoa {
+
+/**
+ * @brief      A subgraph of an existing graph.
+ *
+ * @tparam     GraphType  The type of the graph.
+ */
+template< typename GraphType>
+class Subgraph {
+public:
+    /// @brief The type of the underlying graph.
+    using TUnderlyingGraph = GraphType;
+    using TVertexId = typename TUnderlyingGraph::TVertexId;
+    using TEdgeId = typename TUnderlyingGraph::TEdgeId;
+    using TVerticesView = VectorView<TVertexId, true>;
+    using TEdgesView = VectorView<TEdgeId, true>;
+
+    /**
+     * @brief      The constructor.
+     *
+     * @pre        All vertex identifiers and edge identifiers must correspond
+     *             to existing vertices and edges in the graph, respectively.
+     *
+     * @param      graph     A pointer to the underlying graph.
+     * @param[in]  vertices  The identifiers of the vertices in the subgraph.
+     * @param[in]  edges     The identifiers of the edges in the subgraph.
+     */
+    Subgraph(TUnderlyingGraph * graph,
+             std::vector<TVertexId> vertices,
+             std::vector<TEdgeId> edges)
+    : underlyingGraph_(graph),
+      vertices_(std::move(vertices)),
+      edges_(std::move(edges))
+    {
+        USAGE_ASSERT(std::all_of(vertices_.begin(), vertices_.end(),
+            [this](TVertexId id) {
+                return underlyingGraph_->VertexExists(id);
+            }));
+        USAGE_ASSERT(std::all_of(edges_.begin(), edges_.end(),
+            [this](TEdgeId id) {
+                return underlyingGraph_->EdgeExists(id);
+            }));
+
+        std::sort(vertices_.begin(), vertices_.end());
+        std::sort(edges_.begin(), edges_.end());
+    }
+
+    /**
+     * @brief      The underlying graph.
+     *
+     * @return     A reference to the underlying graph.
+     */
+    TUnderlyingGraph & UnderlyingGraph() {
+        return *underlyingGraph_;
+    }
+
+    /**
+     * @brief      The underlying graph.
+     *
+     * @return     A reference to the underlying graph.
+     */
+    TUnderlyingGraph const & UnderlyingGraph() const {
+        return *underlyingGraph_;
+    }
+
+    /**
+     * @brief      A view on the identifiers of the vertices in the subgraph.
+     *
+     * @details    The identifiers are sorted in increasing order.
+     */
+    TVerticesView Vertices() const {
+        return TVerticesView(&vertices_);
+    }
+
+    /**
+     * @brief      A view on the identifiers of the edges in the subgraph.
+     *
+     * @details    The identifiers are sorted in increasing order.
+     */
+    TEdgesView Edges() const {
+        return TEdgesView(&edges_);
+    }
+
+    friend bool operator==(Subgraph const & lhs, Subgraph const & rhs) {
+        return lhs.underlyingGraph_ == rhs.underlyingGraph_ &&
+               lhs.vertices_ == rhs.vertices_ &&
+               lhs.edges_ == rhs.edges_;
+    }
+
+    friend bool operator!=(Subgraph const & lhs, Subgraph const & rhs) {
+        return !(lhs == rhs);
+    }
+
+private:
+
+    /**
+     * @brief A pointer to the underlying graph.
+     *
+     * @details A pointer is used instead of a reference since otherwise a
+     *          Subgraph object would not be assignable.
+     */
+    TUnderlyingGraph * underlyingGraph_;
+    /**
+     * @brief The identifiers of the vertices belonging to the subgraph.
+     */
+    std::vector<TVertexId> vertices_;
+    /**
+     * @brief The identifiers of the edges belong to the subgraph.
+     */
+    std::vector<TEdgeId> edges_;
+
+};
+
+template<typename GraphType>
+inline std::ostream & operator<<(std::ostream & os,
+                                 Subgraph<GraphType> const & subgraph) {
+    os << "[G="
+       << subgraph.UnderlyingGraph().Name()
+       << ", V="
+       << subgraph.Vertices()
+       << ", E="
+       << subgraph.Edges()
+       << "]";
+    return os;
+}
+
+} // namespace egoa
+
+#endif // EGOA__DATA_STRUCTURES__GRAPHS__SUBGRAPH_HPP