void _K33Search_EmbedBackEdgeToDescendant(graphP theGraph, int RootSide, int RootVertex, int W, int WPrevLink)
{
K33SearchContext *context = NULL;
gp_FindExtension(theGraph, K33SEARCH_ID, (void *)&context);
if (context != NULL)
{
// K33 search may have been attached, but not enabled
if (theGraph->embedFlags == EMBEDFLAGS_SEARCHFORK33)
{
// Get the fwdArc from the adjacentTo field, and use it to get the backArc
int backArc = gp_GetTwinArc(theGraph, gp_GetVertexPertinentEdge(theGraph, W));
// Remove the backArc from the backArcList
if (context->VI[W].backArcList == backArc)
{
if (gp_GetNextArc(theGraph, backArc) == backArc)
context->VI[W].backArcList = NIL;
else context->VI[W].backArcList = gp_GetNextArc(theGraph, backArc);
}
gp_SetNextArc(theGraph, gp_GetPrevArc(theGraph, backArc), gp_GetNextArc(theGraph, backArc));
gp_SetPrevArc(theGraph, gp_GetNextArc(theGraph, backArc), gp_GetPrevArc(theGraph, backArc));
}
// Invoke the superclass version of the function
context->functions.fpEmbedBackEdgeToDescendant(theGraph, RootSide, RootVertex, W, WPrevLink);
}
}
void _AddBackEdge(graphP theGraph, int ancestor, int descendant)
{
int fwdArc, backArc;
/* We get the two edge records of the back edge to embed. */
fwdArc = theGraph->V[ancestor].fwdArcList;
while (gp_IsArc(theGraph, fwdArc))
{
if (theGraph->G[fwdArc].v == descendant)
break;
fwdArc = gp_GetNextArc(theGraph, fwdArc);
if (fwdArc == theGraph->V[ancestor].fwdArcList)
fwdArc = NIL;
}
if (fwdArc == NIL)
return;
backArc = gp_GetTwinArc(theGraph, fwdArc);
/* The forward arc is removed from the fwdArcList of the ancestor. */
if (theGraph->V[ancestor].fwdArcList == fwdArc)
{
if (gp_GetNextArc(theGraph, fwdArc) == fwdArc)
theGraph->V[ancestor].fwdArcList = NIL;
else theGraph->V[ancestor].fwdArcList = gp_GetNextArc(theGraph, fwdArc);
}
gp_SetNextArc(theGraph, gp_GetPrevArc(theGraph, fwdArc), gp_GetNextArc(theGraph, fwdArc));
gp_SetPrevArc(theGraph, gp_GetNextArc(theGraph, fwdArc), gp_GetPrevArc(theGraph, fwdArc));
/* The forward arc is added to the adjacency list of the ancestor. */
gp_SetPrevArc(theGraph, fwdArc, gp_AdjacencyListEndMark(ancestor));
gp_SetNextArc(theGraph, fwdArc, gp_GetFirstArc(theGraph, ancestor));
gp_SetPrevArc(theGraph, gp_GetFirstArc(theGraph, ancestor), fwdArc);
gp_SetFirstArc(theGraph, ancestor, fwdArc);
/* The back arc is added to the adjacency list of the descendant. */
gp_SetPrevArc(theGraph, backArc, gp_AdjacencyListEndMark(descendant));
gp_SetNextArc(theGraph, backArc, gp_GetFirstArc(theGraph, descendant));
gp_SetPrevArc(theGraph, gp_GetFirstArc(theGraph, descendant), backArc);
gp_SetFirstArc(theGraph, descendant, backArc);
theGraph->G[backArc].v = ancestor;
}
void _AddBackEdge(graphP theGraph, int ancestor, int descendant)
{
int fwdArc, backArc;
/* We get the two edge records of the back edge to embed. */
fwdArc = gp_GetVertexFwdArcList(theGraph, ancestor);
while (gp_IsArc(fwdArc))
{
if (gp_GetNeighbor(theGraph, fwdArc) == descendant)
break;
fwdArc = gp_GetNextArc(theGraph, fwdArc);
if (fwdArc == gp_GetVertexFwdArcList(theGraph, ancestor))
fwdArc = NIL;
}
if (gp_IsNotArc(fwdArc))
return;
backArc = gp_GetTwinArc(theGraph, fwdArc);
/* The forward arc is removed from the fwdArcList of the ancestor. */
if (gp_GetVertexFwdArcList(theGraph, ancestor) == fwdArc)
{
if (gp_GetNextArc(theGraph, fwdArc) == fwdArc)
gp_SetVertexFwdArcList(theGraph, ancestor, NIL);
else gp_SetVertexFwdArcList(theGraph, ancestor, gp_GetNextArc(theGraph, fwdArc));
}
gp_SetNextArc(theGraph, gp_GetPrevArc(theGraph, fwdArc), gp_GetNextArc(theGraph, fwdArc));
gp_SetPrevArc(theGraph, gp_GetNextArc(theGraph, fwdArc), gp_GetPrevArc(theGraph, fwdArc));
/* The forward arc is added to the adjacency list of the ancestor. */
gp_SetPrevArc(theGraph, fwdArc, NIL);
gp_SetNextArc(theGraph, fwdArc, gp_GetFirstArc(theGraph, ancestor));
gp_SetPrevArc(theGraph, gp_GetFirstArc(theGraph, ancestor), fwdArc);
gp_SetFirstArc(theGraph, ancestor, fwdArc);
/* The back arc is added to the adjacency list of the descendant. */
gp_SetPrevArc(theGraph, backArc, NIL);
gp_SetNextArc(theGraph, backArc, gp_GetFirstArc(theGraph, descendant));
gp_SetPrevArc(theGraph, gp_GetFirstArc(theGraph, descendant), backArc);
gp_SetFirstArc(theGraph, descendant, backArc);
gp_SetNeighbor(theGraph, backArc, ancestor);
}
/********************************************************************
_CreateBackArcLists()
********************************************************************/
void _CreateBackArcLists(graphP theGraph, K33SearchContext *context)
{
int v, e, eTwin, ancestor;
for (v = gp_GetFirstVertex(theGraph); gp_VertexInRange(theGraph, v); v++)
{
e = gp_GetVertexFwdArcList(theGraph, v);
while (gp_IsArc(e))
{
// Get the ancestor endpoint and the associated back arc
ancestor = gp_GetNeighbor(theGraph, e);
eTwin = gp_GetTwinArc(theGraph, e);
// Put it into the back arc list of the ancestor
if (gp_IsNotArc(context->VI[ancestor].backArcList))
{
context->VI[ancestor].backArcList = eTwin;
gp_SetPrevArc(theGraph, eTwin, eTwin);
gp_SetNextArc(theGraph, eTwin, eTwin);
}
else
{
int eHead = context->VI[ancestor].backArcList;
int eTail = gp_GetPrevArc(theGraph, eHead);
gp_SetPrevArc(theGraph, eTwin, eTail);
gp_SetNextArc(theGraph, eTwin, eHead);
gp_SetPrevArc(theGraph, eHead, eTwin);
gp_SetNextArc(theGraph, eTail, eTwin);
}
// Advance to the next forward edge
e = gp_GetNextArc(theGraph, e);
if (e == gp_GetVertexFwdArcList(theGraph, v))
e = NIL;
}
}
}
int _ReadAdjList(graphP theGraph, FILE *Infile)
{
int N, I, W, ErrorCode, adjList, J;
if (Infile == NULL) return NOTOK;
fgetc(Infile); /* Skip the N= */
fgetc(Infile);
fscanf(Infile, " %d ", &N); /* Read N */
if (gp_InitGraph(theGraph, N) != OK)
{
printf("Failed to init graph");
return NOTOK;
}
// Clear the visited members of the vertices so they can be used
// during the adjacency list read operation
for (I=0; I < N; I++)
theGraph->G[I].visited = 0;
// Do the adjacency list read operation for each vertex in order
for (I = 0, ErrorCode = OK; I < N && ErrorCode==OK; I++)
{
// Read the vertex number
fscanf(Infile, "%d", &theGraph->G[I].v);
// The vertices are expected to be in numeric ascending order
if (theGraph->G[I].v != I)
return NOTOK;
// Skip the colon after the vertex number
fgetc(Infile);
// If the vertex already has a non-empty adjacency list, then it is
// the result of adding edges during processing of preceding vertices.
// The list is removed from the current vertex I and saved for use
// during the read operation for I. Adjacencies to preceding vertices
// are pulled from this list, if present, or added as directed edges
// if not. Adjacencies to succeeding vertices are added as undirected
// edges, and will be corrected later if the succeeding vertex does not
// have the matching adjacency using the following mechanism. After the
// read operation for a vertex I, any adjacency nodes left in the saved
// list are converted to directed edges from the preceding vertex to I.
adjList = gp_GetFirstArc(theGraph, I);
if (gp_IsArc(theGraph, adjList))
{
// Store the adjacency node location in the visited member of each
// of the preceding vertices to which I is adjacent so that we can
// efficiently detect the adjacency during the read operation and
// efficiently find the adjacency node.
J = gp_GetFirstArc(theGraph, I);
while (gp_IsArc(theGraph, J))
{
theGraph->G[theGraph->G[J].v].visited = J;
J = gp_GetNextArc(theGraph, J);
}
// Make the adjacency list circular, for later ease of processing
gp_SetPrevArc(theGraph, adjList, gp_GetLastArc(theGraph, I));
gp_SetNextArc(theGraph, gp_GetLastArc(theGraph, I), adjList);
// Remove the list from the vertex
gp_SetFirstArc(theGraph, I, gp_AdjacencyListEndMark(I));
gp_SetLastArc(theGraph, I, gp_AdjacencyListEndMark(I));
}
// Read the adjacency list.
while (1)
{
// Read the next adjacent vertex, with NIL indicating the list end
fscanf(Infile, " %d ", &W);
if (W < 0) break;
// Vertex numbers must be less than N
if (W >= N)
ErrorCode = NOTOK;
// Loop edges are not supported, but no reason to throw an error if they occur
// If a loop occurs, we just do like the ostrich and ignore it
else if (W == I)
ErrorCode = OK;
// If the adjacency is to a succeeding, higher numbered vertex,
// then we'll add an undirected edge for now
else if (I < W)
{
ErrorCode = gp_AddEdge(theGraph, I, 0, W, 0);
}
// If the adjacency is to a preceding, lower numbered vertex, then
// we have to pull the adjacency node from the preexisting adjList,
// if it is there, and if not then we have to add a directed edge.
else
{
// If the adjacency node (arc) already exists, then we add it
// as the new first arc of the vertex and delete it from adjList
if (theGraph->G[W].visited)
{
J = theGraph->G[W].visited;
// Remove the arc J from the adjList construct
theGraph->G[W].visited = 0;
if (adjList == J)
{
if ((adjList = gp_GetNextArc(theGraph, J)) == J)
adjList = NIL;
}
gp_SetPrevArc(theGraph, gp_GetNextArc(theGraph, J), gp_GetPrevArc(theGraph, J));
gp_SetNextArc(theGraph, gp_GetPrevArc(theGraph, J), gp_GetNextArc(theGraph, J));
gp_AttachFirstArc(theGraph, I, J);
}
// If an adjacency node to the lower numbered vertex W does not
// already exist, then we make a new directed arc from the current
// vertex I to W.
else
{
// It is added as the new first arc in both vertices
ErrorCode = gp_AddEdge(theGraph, I, 0, W, 0);
if (ErrorCode == OK)
// Note that this call also sets OUTONLY on the twin arc
gp_SetDirection(theGraph, gp_GetFirstArc(theGraph, W), EDGEFLAG_DIRECTION_INONLY);
}
}
if (ErrorCode != OK) break;
}
// If there are still adjList entries after the read operation
// then those entries are not representative of full undirected edges.
// Rather, they represent incoming directed arcs from other vertices
// into vertex I. They need to be added back into I's adjacency list but
// marked as "INONLY", while the twin is marked "OUTONLY" (by the same function).
while (gp_IsArc(theGraph, adjList))
{
J = adjList;
theGraph->G[theGraph->G[J].v].visited = 0;
if ((adjList = gp_GetNextArc(theGraph, J)) == J)
adjList = NIL;
gp_SetPrevArc(theGraph, gp_GetNextArc(theGraph, J), gp_GetPrevArc(theGraph, J));
gp_SetNextArc(theGraph, gp_GetPrevArc(theGraph, J), gp_GetNextArc(theGraph, J));
gp_AttachFirstArc(theGraph, I, J);
gp_SetDirection(theGraph, J, EDGEFLAG_DIRECTION_INONLY);
}
}
return ErrorCode;
}
int _K33Search_CreateFwdArcLists(graphP theGraph)
{
K33SearchContext *context = NULL;
gp_FindExtension(theGraph, K33SEARCH_ID, (void *)&context);
if (context == NULL)
return NOTOK;
// For isolating a K_{3,3} homeomorph, we need the forward edges
// of each vertex to be in sorted order by DFI of descendants.
// Otherwise we just drop through to the normal processing...
if (theGraph->embedFlags == EMBEDFLAGS_SEARCHFORK33)
{
int I, Jcur, Jnext, ancestor;
// for each vertex v in order, we follow each of its back edges
// to the twin forward edge in an ancestor u, then we move
// the forward edge to the fwdArcList of u. Since this loop
// processes vertices in order, the fwdArcList of each vertex
// will be in order by the neighbor indicated by the forward edges.
for (I=0; I < theGraph->N; I++)
{
// Skip this vertex if it has no edges
Jnext = gp_GetLastArc(theGraph, I);
if (!gp_IsArc(theGraph, Jnext))
continue;
// Skip the forward edges, which are in succession at the
// end of the arc list (last and its predecessors)
while (theGraph->G[Jnext].type == EDGE_FORWARD)
Jnext = gp_GetPrevArc(theGraph, Jnext);
// Now we want to put all the back arcs in a backArcList, too.
// Since we've already skipped past the forward arcs, we continue
// with the predecessor arcs until we either run out of arcs or
// we find a DFS child arc (the DFS child arcs are in succession
// at the beginning of the arc list, so when a child arc is
// encountered in the predecessor direction, then there won't be
// any more back arcs.
while (gp_IsArc(theGraph, Jnext) &&
theGraph->G[Jnext].type != EDGE_DFSCHILD)
{
Jcur = Jnext;
Jnext = gp_GetPrevArc(theGraph, Jnext);
if (theGraph->G[Jcur].type == EDGE_BACK)
{
// Remove the back arc from I's adjacency list
gp_DetachArc(theGraph, Jcur);
// Put the back arc in the backArcList
if (context->V[I].backArcList == NIL)
{
context->V[I].backArcList = Jcur;
gp_SetPrevArc(theGraph, Jcur, Jcur);
gp_SetNextArc(theGraph, Jcur, Jcur);
}
else
{
gp_AttachArc(theGraph, NIL, context->V[I].backArcList, 1, Jcur);
}
// Determine the ancestor of vertex I to which Jcur connects
ancestor = theGraph->G[Jcur].v;
// Go to the forward arc in the ancestor
Jcur = gp_GetTwinArc(theGraph, Jcur);
// Remove the forward arc from the ancestor's adjacency list
gp_DetachArc(theGraph, Jcur);
// Add the forward arc to the end of the fwdArcList.
if (theGraph->V[ancestor].fwdArcList == NIL)
{
theGraph->V[ancestor].fwdArcList = Jcur;
gp_SetPrevArc(theGraph, Jcur, Jcur);
gp_SetNextArc(theGraph, Jcur, Jcur);
}
else
{
gp_AttachArc(theGraph, NIL, theGraph->V[ancestor].fwdArcList, 1, Jcur);
}
}
}
}
// Since the fwdArcLists have been created, we do not fall through
// to run the superclass implementation
return OK;
}
// If we're not actually running a K3,3 search, then we just run the
// superclass implementation
return context->functions.fpCreateFwdArcLists(theGraph);
}
