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Full Discussion: [C] deleting node from graph
Top Forums Programming [C] deleting node from graph Post 302531930 by Loic Domaigne on Sunday 19th of June 2011 12:15:58 AM
Old 06-19-2011
Quote:
So I suppose doing it the opposite way is not correct, but why?
Because:
  • you're freeing G->adj[i], not G->adj[u].
  • If you would free G->adj[u], the pointer wouldn't be correct since you have already shifted.
You could perhaps get your code working by saving G->adj[u] before the shift; and then deleting it.

As your graph is undirected, there is many possible improvements. I'll try to post a few ideas tomorrow. But for now, it's bed time Smilie

Cheers, Loïc

---------- Post updated 06-19-11 at 06:15 AM ---------- Previous update was 06-18-11 at 10:31 PM ----------

Hi Luke,

here a few idea to improve the algorithm performance, given your data structure and the fact that the graph is undirected:
  • instead of visiting of node of the graph to check if it has an edge to the node to delete, it is more efficient to only visit the nodes given in the adjacency list of node u.
  • you don't need recursive function to remove the edge (u,v). Instead:
    Code:
    prev=NULL;
for (p=G->adj[v]; p && p->key!=u; prev=p, p=p->next);
if (prev==NULL) G->adj[v]=p->next; else prev->next = p->next;

  • you could perhaps try memmove() to shift the G->adj array. This should be equivalent to your shift operation, but eventually memmove() implementation is faster, because the libc designers usually take advantage of the underlying hardware (e.g. SSE instructions).
    Code:
    if (u!=G->nv-1) memmove(G->adj[u], G->adj[u+1], (G->nv-u-1)*sizeof(edge*));

I don't know however if your data structure is the most suited for what you're targeting, but perhaps can Mrs. Google help you further...

HTH, Loïc
 

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LEARN ABOUT DEBIAN

graph1

struct::graph1(3tcl)						Tcl Data Structures					      struct::graph1(3tcl)

__________________________________________________________________________________________________________________________________________________

NAME

       struct::graph1 - Create and manipulate directed graph objects (version 1)

SYNOPSIS

       package require Tcl  8.2

       package require struct::graph  ?1.2.1?

       graphName option ?arg arg ...?

       graphName destroy

       graphName arc append arc ?-key key? value

       graphName arc delete arc ?arc ...?

       graphName arc exists arc

       graphName arc get arc ?-key key?

       graphName arc getall arc

       graphName arc keys arc

       graphName arc keyexists arc ?-key key?

       graphName arc insert start end ?child?

       graphName arc lappend arc ?-key key? value

       graphName arc set arc ?-key key? ?value?

       graphName arc source arc

       graphName arc target arc

       graphName arc unset arc ?-key key?

       graphName arcs ?-key key? ?-value value? ?-in|-out|-adj|-inner|-embedding nodelist?

       graphName node append node ?-key key? value

       graphName node degree ?-in|-out? node

       graphName node delete node ?node ...?

       graphName node exists node

       graphName node get node ?-key key?

       graphName node getall node

       graphName node keys node

       graphName node keyexists node ?-key key?

       graphName node insert ?child?

       graphName node lappend node ?-key key? value

       graphName node opposite node arc

       graphName node set node ?-key key? ?value?

       graphName node unset node ?-key key?

       graphName nodes ?-key key? ?-value value? ?-in|-out|-adj|-inner|-embedding nodelist?

       graphName get ?-key key?

       graphName getall

       graphName keys

       graphName keyexists ?-key key?

       graphName set ?-key key? ?value?

       graphName swap node1 node2

       graphName unset ?-key key?

       graphName walk node ?-order order? ?-type type? ?-dir direction? -command cmd

_________________________________________________________________

DESCRIPTION

       The  ::struct::graph command creates a new graph object with an associated global Tcl command whose name is graphName.  This command may be
       used to invoke various operations on the graph.	It has the following general form:

       graphName option ?arg arg ...?
	      Option and the args determine the exact behavior of the command.

       A directed graph is a structure containing two collections of elements, called nodes and arcs respectively, together with a relation ("con-
       nectivity") that places a general structure upon the nodes and arcs.

       Each  arc  is  connected  to  two nodes, one of which is called the source and the other the target. This imposes a direction upon the arc,
       which is said to go from the source to the target. It is allowed that source and target of an arc are the same node. Such an arc is  called
       a loop. Whenever a node is source or target of an arc both are said to be adjacent. This extends into a relation between nodes, i.e. if two
       nodes are connected through at least one arc they are said to be adjacent too.

       Each node can be the source and target for any number of arcs. The former are called the outgoing arcs of the node, the latter the incoming
       arcs of the node. The number of edges in either set is called the in- resp. the out-degree of the node.

       In  addition  to  maintaining  the node and arc relationships, this graph implementation allows any number of keyed values to be associated
       with each node and arc.

       The following commands are possible for graph objects:

       graphName destroy
	      Destroy the graph, including its storage space and associated command.

       graphName arc append arc ?-key key? value
	      Appends a value to one of the keyed values associated with an arc. If no key is specified, the key data is assumed.

       graphName arc delete arc ?arc ...?
	      Remove the specified arcs from the graph.

       graphName arc exists arc
	      Return true if the specified arc exists in the graph.

       graphName arc get arc ?-key key?
	      Return the value associated with the key key for the arc.  If no key is specified, the key data is assumed.

       graphName arc getall arc
	      Returns a serialized list of key/value pairs (suitable for use with [array set]) for the arc.

       graphName arc keys arc
	      Returns a list of keys for the arc.

       graphName arc keyexists arc ?-key key?
	      Return true if the specified key exists for the arc. If no key is specified, the key data is assumed.

       graphName arc insert start end ?child?
	      Insert an arc named child into the graph beginning at the node start and ending at the node end. If the name of the new arc  is  not
	      specified the system will generate a unique name of the form arcx.

       graphName arc lappend arc ?-key key? value
	      Appends a value (as a list) to one of the keyed values associated with an arc.  If no key is specified, the key data is assumed.

       graphName arc set arc ?-key key? ?value?
	      Set or get one of the keyed values associated with an arc.  If no key is specified, the key data is assumed.  Each arc that is added
	      to a graph has the empty string assigned to the key data automatically.  An arc may have any number of keyed values associated  with
	      it.   If	value  is  not	specified, this command returns the current value assigned to the key; if value is specified, this command
	      assigns that value to the key.

       graphName arc source arc
	      Return the node the given arc begins at.

       graphName arc target arc
	      Return the node the given arc ends at.

       graphName arc unset arc ?-key key?
	      Remove a keyed value from the arc arc.  If no key is specified, the key data is assumed.

       graphName arcs ?-key key? ?-value value? ?-in|-out|-adj|-inner|-embedding nodelist?
	      Return a list of arcs in the graph. If no restriction is specified a list containing all arcs is returned.  Restrictions	can  limit
	      the  list  of  returned arcs based on the nodes that are connected by the arc, on the keyed values associated with the arc, or both.
	      The restrictions that involve connected nodes have a list of nodes as argument, specified after the name of the restriction itself.

	      -in    Return a list of all arcs whose target is one of the nodes in the nodelist.

	      -out   Return a list of all arcs whose source is one of the nodes in the nodelist.

	      -adj   Return a list of all arcs adjacent to at least one of the nodes in the nodelist. This is the union of the nodes  returned	by
		     -in and -out.

	      -inner Return  a	list  of all arcs adjacent to two of the nodes in the nodelist. This is the set of arcs in the subgraph spawned by
		     the specified nodes.

	      -embedding
		     Return a list of all arcs adjacent to exactly one of the nodes in the nodelist. This is the set of arcs connecting  the  sub-
		     graph spawned by the specified nodes to the rest of the graph.

	      -key key
		     Limit the list of arcs that are returned to those arcs that have an associated key key.

	      -value value
		     This  restriction can only be used in combination with -key. It limits the list of arcs that are returned to those arcs whose
		     associated key key has the value value.

       The restrictions imposed by either -in, -out, -adj, -inner, or -embedded are applied first. Specifying more than one of	them  is  illegal.
       At last the restrictions set via -key (and -value) are applied.	Specifying more than one -key (and -value) is illegal.

       graphName node append node ?-key key? value
	      Appends a value to one of the keyed values associated with an node. If no key is specified, the key data is assumed.

       graphName node degree ?-in|-out? node
	      Return  the  number  of arcs adjacent to the specified node. If one of the restrictions -in or -out is given only the incoming resp.
	      outgoing arcs are counted.

       graphName node delete node ?node ...?
	      Remove the specified nodes from the graph.  All of the nodes' arcs will be removed as well to prevent unconnected arcs.

       graphName node exists node
	      Return true if the specified node exists in the graph.

       graphName node get node ?-key key?
	      Return the value associated with the key key for the node.  If no key is specified, the key data is assumed.

       graphName node getall node
	      Returns a serialized list of key/value pairs (suitable for use with [array set]) for the node.

       graphName node keys node
	      Returns a list of keys for the node.

       graphName node keyexists node ?-key key?
	      Return true if the specified key exists for the node. If no key is specified, the key data is assumed.

       graphName node insert ?child?
	      Insert a node named child into the graph. The nodes has no arcs connected to it. If the name of the new child is not  specified  the
	      system will generate a unique name of the form nodex.

       graphName node lappend node ?-key key? value
	      Appends a value (as a list) to one of the keyed values associated with an node. If no key is specified, the key data is assumed.

       graphName node opposite node arc
	      Return the node at the other end of the specified arc, which has to be adjacent to the given node.

       graphName node set node ?-key key? ?value?
	      Set  or  get  one  of  the keyed values associated with a node.  If no key is specified, the key data is assumed.  Each node that is
	      added to a graph has the empty string assigned to the key data automatically.  A node may have any number of keyed values associated
	      with it.	If value is not specified, this command returns the current value assigned to the key; if value is specified, this command
	      assigns that value to the key.

       graphName node unset node ?-key key?
	      Remove a keyed value from the node node.	If no key is specified, the key data is assumed.

       graphName nodes ?-key key? ?-value value? ?-in|-out|-adj|-inner|-embedding nodelist?
	      Return a list of nodes in the graph. Restrictions can limit the list of returned nodes based on neighboring nodes, or based  on  the
	      keyed  values  associated with the node. The restrictions that involve neighboring nodes have a list of nodes as argument, specified
	      after the name of the restriction itself.

	      The possible restrictions are the same as for method arcs. The set of nodes to return is computed as the union  of  all  source  and
	      target nodes for all the arcs satisfying the restriction as defined for arcs.

       graphName get ?-key key?
	      Return the value associated with the key key for the graph. If no key is specified, the key data is assumed.

       graphName getall
	      Returns a serialized list of key/value pairs (suitable for use with [array set]) for the whole graph.

       graphName keys
	      Returns a list of keys for the whole graph.

       graphName keyexists ?-key key?
	      Return true if the specified key exists for the whole graph. If no key is specified, the key data is assumed.

       graphName set ?-key key? ?value?
	      Set  or  get  one  of  the keyed values associated with a graph. If no key is specified, the key data is assumed. Each graph has the
	      empty string assigned to the key data automatically. A graph may have any number of keyed values associated with it. If value is not
	      specified, this command returns the current value assigned to the key; if value is specified, this command assigns that value to the
	      key.

       graphName swap node1 node2
	      Swap the position of node1 and node2 in the graph.

       graphName unset ?-key key?
	      Remove a keyed value from the graph. If no key is specified, the key data is assumed.

       graphName walk node ?-order order? ?-type type? ?-dir direction? -command cmd
	      Perform a breadth-first or depth-first walk of the graph starting at the node node going in either  the  direction  of  outgoing	or
	      opposite to the incoming arcs.

	      The  type  of  walk,  breadth-first  or  depth-first, is determined by the value of type; bfs indicates breadth-first, dfs indicates
	      depth-first.  Depth-first is the default.

	      The order of the walk, pre-order, post-order or both-order is determined by the value of order; pre indicates pre-order, post  indi-
	      cates  post-order, both indicates both-order. Pre-order is the default. Pre-order walking means that a node is visited before any of
	      its neighbors (as defined by the direction, see below). Post-order walking means that a parent is visited after any  of  its  neigh-
	      bors.  Both-order  walking means that a node is visited before and after any of its neighbors. The combination of a bread-first walk
	      with post- or both-order is illegal.

	      The direction of the walk is determined by the value of dir; backward indicates the direction opposite to the incoming arcs, forward
	      indicates the direction of the outgoing arcs.

	      As the walk progresses, the command cmd will be evaluated at each node, with the mode of the call (enter or leave) and values graph-
	      Name and the name of the current node appended. For a pre-order walk, all nodes are entered, for a post-order all nodes are left. In
	      a both-order walk the first visit of a node enters it, the second visit leaves it.

BUGS, IDEAS, FEEDBACK
       This  document,	and the package it describes, will undoubtedly contain bugs and other problems.  Please report such in the category struct
       :: graph of the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you may
       have for either package and/or documentation.

KEYWORDS

       cgraph, graph

CATEGORY

       Data structures

COPYRIGHT

       Copyright (c) 2002 Andreas Kupries <andreas_kupries@users.sourceforge.net>

struct								       1.2.1						      struct::graph1(3tcl)
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