MaximumPlanarSubgraph.h

Go to the documentation of this file.

 
#pragma once
 
#include <ogdf/basic/Module.h>
#include <ogdf/basic/Timeouter.h>
#include <ogdf/basic/extended_graph_alg.h>
#include <ogdf/basic/simple_graph_alg.h>
#include <ogdf/cluster/ClusterGraph.h>
#include <ogdf/cluster/MaximumCPlanarSubgraph.h>
#include <ogdf/planarity/PlanarSubgraphModule.h>
 
#include <ogdf/external/abacus.h>
 
namespace ogdf {
 
 
template<typename TCost>
class MaximumPlanarSubgraph : public PlanarSubgraphModule<TCost> {
public:
    // Construction
    MaximumPlanarSubgraph() { }
 
    // Destruction
    virtual ~MaximumPlanarSubgraph() { }
 
    virtual MaximumPlanarSubgraph* clone() const override { return new MaximumPlanarSubgraph(); }
 
protected:
    // Implements the Planar Subgraph interface.
    // For the given graph \p G, a clustered graph with only
    // a single root cluster is generated.
    // Computes set of edges delEdges, which have to be deleted
    // in order to get a planar subgraph; edges in preferredEdges
    // should be contained in planar subgraph.
    // Status: pCost and preferredEdges are ignored in current implementation.
    virtual Module::ReturnType doCall(const Graph& G, const List<edge>& preferredEdges,
            List<edge>& delEdges, const EdgeArray<TCost>* pCost, bool preferredImplyPlanar) override {
        if (G.numberOfEdges() < 9) {
            return Module::ReturnType::Optimal;
        }
 
        //if the graph is planar, we don't have to do anything
        if (isPlanar(G)) {
            return Module::ReturnType::Optimal;
        }
 
        //Exact ILP
        MaximumCPlanarSubgraph mc;
 
        delEdges.clear();
 
        NodeArray<node> tableNodes(G, nullptr);
        EdgeArray<edge> tableEdges(G, nullptr);
        NodeArray<bool> mark(G, 0);
 
        EdgeArray<int> componentID(G);
 
        // Determine biconnected components
        int bcCount = biconnectedComponents(G, componentID);
        OGDF_ASSERT(bcCount >= 1);
 
        // Determine edges per biconnected component
        Array<SList<edge>> blockEdges(0, bcCount - 1);
        for (edge e : G.edges) {
            if (!e->isSelfLoop()) {
                blockEdges[componentID[e]].pushFront(e);
            }
        }
 
        // Determine nodes per biconnected component.
        Array<SList<node>> blockNodes(0, bcCount - 1);
        int i;
        for (i = 0; i < bcCount; i++) {
            for (edge e : blockEdges[i]) {
                if (!mark[e->source()]) {
                    blockNodes[i].pushBack(e->source());
                    mark[e->source()] = true;
                }
                if (!mark[e->target()]) {
                    blockNodes[i].pushBack(e->target());
                    mark[e->target()] = true;
                }
            }
            for (node v : blockNodes[i]) {
                mark[v] = false;
            }
        }
 
 
        // Perform computation for every biconnected component
        Module::ReturnType mr;
        if (bcCount == 1) {
            mr = callWithDouble(mc, G, pCost, delEdges);
        } else {
            for (i = 0; i < bcCount; i++) {
                Graph C;
 
                for (node v : blockNodes[i]) {
                    node w = C.newNode();
                    tableNodes[v] = w;
                }
 
                EdgeArray<double> cost(C);
 
                for (edge e : blockEdges[i]) {
                    edge f = C.newEdge(tableNodes[e->source()], tableNodes[e->target()]);
                    tableEdges[e] = f;
                    if (pCost != nullptr) {
                        cost[tableEdges[e]] = (*pCost)[e];
                    }
                }
 
                // Construct a translation table for the edges.
                // Necessary, since edges are deleted in a new graph
                // that represents the current biconnected component
                // of the original graph.
                EdgeArray<edge> backTableEdges(C, nullptr);
                for (edge e : blockEdges[i]) {
                    backTableEdges[tableEdges[e]] = e;
                }
 
                // The deleted edges of the biconnected component
                List<edge> delEdgesOfBC;
 
                ClusterGraph CG(C);
                mr = mc.call(CG, pCost == nullptr ? nullptr : &cost, delEdgesOfBC);
 
                // Abort if no optimal solution found, i.e., feasible is also not allowed
                if (mr != Module::ReturnType::Optimal) {
                    break;
                }
 
                // Get the original edges that are deleted and
                // put them on the list delEdges.
                while (!delEdgesOfBC.empty()) {
                    delEdges.pushBack(backTableEdges[delEdgesOfBC.popFrontRet()]);
                }
            }
        }
        return mr;
    }
 
 
private:
    // Call algorithm with costs as double. All underlying algorithms cast the costs to double on use eventually.
    // However, only convert the costs if they are not given as double already.
    template<typename U = TCost>
    Module::ReturnType callWithDouble(MaximumCPlanarSubgraph& mc, const Graph& G,
            const EdgeArray<U>* pCost, List<edge>& delEdges) {
        if (pCost == nullptr) {
            return callWithDouble(mc, G, nullptr, delEdges);
        } else {
            EdgeArray<double> dCost(G);
            for (auto it = pCost->begin(); it != pCost->end(); ++it) {
                dCost[it.key()] = it.value();
            }
            return callWithDouble(mc, G, &dCost, delEdges);
        }
    }
 
    Module::ReturnType callWithDouble(MaximumCPlanarSubgraph& mc, const Graph& G,
            const EdgeArray<double>* pCost, List<edge>& delEdges) {
        ClusterGraph CG(G);
        return mc.call(CG, pCost, delEdges);
    }
};
 
}