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/*
* glade-tsort.c: a topological sorting algorithm implementation
*
* Copyright (C) 2013 Juan Pablo Ugarte.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* Authors:
* Juan Pablo Ugarte <juanpablougarte@gmail.com>
*/
#include "glade-tsort.h"
/**
* _node_edge_prepend:
* @node: a _NodeEdge pointer or NULL
* @predecessor:
* @successor:
*
* Adds a new node with the values @predecessor and @successor to the start of
* @node list.
*
* Returns: the new start of the node list.
*/
GList *
_node_edge_prepend (GList *list,
gpointer predecessor,
gpointer successor)
{
_NodeEdge *edge = g_slice_new (_NodeEdge);
edge->predecessor = predecessor;
edge->successor = successor;
return g_list_prepend (list, edge);
}
static void
_node_edge_free (gpointer data)
{
g_slice_free (_NodeEdge, data);
}
void
_node_edge_list_free (GList *list)
{
g_list_free_full (list, _node_edge_free);
}
static inline void
tsort_remove_non_start_nodes (GList **nodes, GList *edges)
{
GList *l;
for (l = edges; l; l = g_list_next (l))
{
_NodeEdge *edge = l->data;
*nodes = g_list_remove (*nodes, edge->successor);
}
}
static inline gboolean
tsort_node_has_no_incoming_edge (gpointer node, GList *edges)
{
GList *l;
for (l = edges; l; l = g_list_next (l))
{
_NodeEdge *edge = l->data;
if (node == edge->successor)
return FALSE;
}
return TRUE;
}
/**
* _glade_tsort:
* @nodes: list of pointers to sort
* @edges: pointer to the list of #_NodeEdge that conform the dependency
* graph of @nodes.
*
* Topological sorting implementation.
* After calling this function only graph cycles (circular dependencies) are left
* in @edges list. So if @edges is NULL it means the returned list has all the
* elements topologically sorted if not it means there are at least one
* circular dependency.
*
* L ← Empty list that will contain the sorted elements
* S ← Set of all nodes with no incoming edges
* while S is non-empty do
* remove a node n from S
* insert n into L
* for each node m with an edge e from n to m do
* remove edge e from the graph
* if m has no other incoming edges then
* insert m into S
* return L (a topologically sorted order if graph has no edges)
*
* see: http://en.wikipedia.org/wiki/Topological_sorting
*
* Returns: a new list sorted by dependency including nodes only present in @edges
*/
GList *
_glade_tsort (GList **nodes, GList **edges)
{
GList *sorted_nodes;
/* L ← Empty list that will contain the sorted elements */
sorted_nodes = NULL;
/* S ← Set of all nodes with no incoming edges */
tsort_remove_non_start_nodes (nodes, *edges);
/* while S is non-empty do */
while (*nodes)
{
GList *l, *next;
gpointer n;
/* remove a node n from S */
n = (*nodes)->data;
*nodes = g_list_delete_link (*nodes, *nodes);
/* insert n into L */
/*if (!glade_widget_get_parent (n)) this would be a specific optimization */
sorted_nodes = g_list_prepend (sorted_nodes, n);
/* for each node m ... */
for (l = *edges; l; l = next)
{
_NodeEdge *edge = l->data;
next = g_list_next (l);
/* ... with an edge e from n to m do */
if (edge->predecessor == n)
{
/* remove edge e from the graph */
*edges = g_list_delete_link (*edges, l);
/* if m has no other incoming edges then */
if (tsort_node_has_no_incoming_edge (edge->successor, *edges))
/* insert m into S */
*nodes = g_list_prepend (*nodes, edge->successor);
g_slice_free (_NodeEdge, edge);
}
}
}
/* if graph has edges then return error (graph has at least one cycle) */
#if 0 /* We rather not return NULL, caller must check if edge */
if (*edges)
{
g_list_free (sorted_nodes);
_node_edge_list_free (*edges);
*edges = NULL;
return NULL;
}
#endif
/* return L (a topologically sorted order if edge is NULL) */
return g_list_reverse (sorted_nodes);
}
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