subgraph.cpp

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namespace TSnap {

// Graph Algorithms

// RenumberNodes ... Renumber node ids in the subgraph to 0...N-1
PUNGraph GetSubGraph(const PUNGraph& Graph, const TIntV& NIdV, const bool& RenumberNodes) {
  //if (! RenumberNodes) { return TSnap::GetSubGraph(Graph, NIdV); }
  PUNGraph NewGraphPt = TUNGraph::New();
  TUNGraph& NewGraph = *NewGraphPt;
  NewGraph.Reserve(NIdV.Len(), -1);
  TIntSet NIdSet(NIdV.Len());
  for (int n = 0; n < NIdV.Len(); n++) {
    if (Graph->IsNode(NIdV[n])) {
      NIdSet.AddKey(NIdV[n]);
      if (! RenumberNodes) { NewGraph.AddNode(NIdV[n]); }
      else { NewGraph.AddNode(NIdSet.GetKeyId(NIdV[n])); }
    }
  }
  if (! RenumberNodes) {
    for (int n = 0; n < NIdSet.Len(); n++) {
      const int SrcNId = NIdSet[n];
      const TUNGraph::TNodeI NI = Graph->GetNI(SrcNId);
      for (int edge = 0; edge < NI.GetOutDeg(); edge++) {
        const int OutNId = NI.GetOutNId(edge);
        if (NIdSet.IsKey(OutNId)) {
          NewGraph.AddEdge(SrcNId, OutNId); }
      }
    }
  } else {
    for (int n = 0; n < NIdSet.Len(); n++) {
      const int SrcNId = NIdSet[n];
      const TUNGraph::TNodeI NI = Graph->GetNI(SrcNId);
      for (int edge = 0; edge < NI.GetOutDeg(); edge++) {
        const int OutNId = NI.GetOutNId(edge);
        if (NIdSet.IsKey(OutNId)) {
          NewGraph.AddEdge(NIdSet.GetKeyId(SrcNId), NIdSet.GetKeyId(OutNId)); }
      }
    }
  }
  return NewGraphPt;
}

// RenumberNodes ... Renumber node ids in the subgraph to 0...N-1
PNGraph GetSubGraph(const PNGraph& Graph, const TIntV& NIdV, const bool& RenumberNodes) {
  //if (! RenumberNodes) { return TSnap::GetSubGraph(Graph, NIdV); }
  PNGraph NewGraphPt = TNGraph::New();
  TNGraph& NewGraph = *NewGraphPt;
  NewGraph.Reserve(NIdV.Len(), -1);
  TIntSet NIdSet(NIdV.Len());
  for (int n = 0; n < NIdV.Len(); n++) {
    if (Graph->IsNode(NIdV[n])) {
      NIdSet.AddKey(NIdV[n]);
      if (! RenumberNodes) { NewGraph.AddNode(NIdV[n]); }
      else { NewGraph.AddNode(NIdSet.GetKeyId(NIdV[n])); }
    }
  }
  if (! RenumberNodes) {
    for (int n = 0; n < NIdSet.Len(); n++) {
      const int SrcNId = NIdSet[n];
      const TNGraph::TNodeI NI = Graph->GetNI(SrcNId);
      for (int edge = 0; edge < NI.GetOutDeg(); edge++) {
        const int OutNId = NI.GetOutNId(edge);
        if (NIdSet.IsKey(OutNId)) {
          NewGraph.AddEdge(SrcNId, OutNId); }
      }
    }
  } else {
    for (int n = 0; n < NIdSet.Len(); n++) {
      const int SrcNId = NIdSet[n];
      const TNGraph::TNodeI NI = Graph->GetNI(SrcNId);
      for (int edge = 0; edge < NI.GetOutDeg(); edge++) {
        const int OutNId = NI.GetOutNId(edge);
        if (NIdSet.IsKey(OutNId)) {
          NewGraph.AddEdge(NIdSet.GetKeyId(SrcNId), NIdSet.GetKeyId(OutNId)); }
      }
    }
  }
  return NewGraphPt;
}


} // namespace TSnap