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);
}
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;
}
