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Revert changes to Kruskal's algo.

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This commit is contained in:
Guus Sliepen 2002-03-12 16:30:15 +00:00
parent f219f156cf
commit 4b3aef9e69
1 changed files with 36 additions and 9 deletions
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43
src/graph.c
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@ -17,7 +17,7 @@
along with this program; if not, write to the Free Software along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
$Id: graph.c,v 1.1.2.8 2002/03/12 13:42:23 guus Exp $ $Id: graph.c,v 1.1.2.9 2002/03/12 16:30:15 guus Exp $
*/ */
/* We need to generate two trees from the graph: /* We need to generate two trees from the graph:
@ -32,7 +32,9 @@
favour Kruskal's, because we make an extra AVL tree of edges sorted on favour Kruskal's, because we make an extra AVL tree of edges sorted on
weights (metric). That tree only has to be updated when an edge is added or weights (metric). That tree only has to be updated when an edge is added or
removed, and during the MST algorithm we just have go linearly through that removed, and during the MST algorithm we just have go linearly through that
tree. tree, adding safe edges until #edges = #nodes - 1. The implementation here
however is not so fast, because I tried to avoid having to make a forest and
merge trees.
For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
simple breadth-first search is presented here. simple breadth-first search is presented here.
@ -60,17 +62,20 @@
#include "system.h" #include "system.h"
/* Kruskal's minimum spanning tree algorithm. /* Implementation of Kruskal's algorithm.
Running time: O(E) Running time: O(EN)
Edges are already sorted on weight. Please note that sorting on weight is already done by add_edge().
*/ */
void mst_kruskal(void) void mst_kruskal(void)
{ {
avl_node_t *node; avl_node_t *node, *next;
edge_t *e; edge_t *e;
node_t *n; node_t *n;
connection_t *c; connection_t *c;
int nodes = 0;
int safe_edges = 0;
int skipped;
/* Clear MST status on connections */ /* Clear MST status on connections */
@ -85,12 +90,16 @@ void mst_kruskal(void)
if(!edge_weight_tree->head) if(!edge_weight_tree->head)
return; return;
if(debug_lvl >= DEBUG_SCARY_THINGS)
syslog(LOG_DEBUG, "Running Kruskal's algorithm:");
/* Clear visited status on nodes */ /* Clear visited status on nodes */
for(node = node_tree->head; node; node = node->next) for(node = node_tree->head; node; node = node->next)
{ {
n = (node_t *)node->data; n = (node_t *)node->data;
n->status.visited = 0; n->status.visited = 0;
nodes++;
} }
/* Starting point */ /* Starting point */
@ -99,18 +108,36 @@ void mst_kruskal(void)
/* Add safe edges */ /* Add safe edges */
for(node = edge_weight_tree->head; node; node = node->next) for(skipped = 0, node = edge_weight_tree->head; node; node = next)
{ {
next = node->next;
e = (edge_t *)node->data; e = (edge_t *)node->data;
if(e->from.node->status.visited && e->to.node->status.visited) if(e->from.node->status.visited == e->to.node->status.visited)
{
skipped = 1;
continue; continue;
}
e->from.node->status.visited = 1; e->from.node->status.visited = 1;
e->to.node->status.visited = 1; e->to.node->status.visited = 1;
if(e->connection) if(e->connection)
e->connection->status.mst = 1; e->connection->status.mst = 1;
safe_edges++;
if(debug_lvl >= DEBUG_SCARY_THINGS)
syslog(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from.node->name, e->to.node->name, e->weight);
if(skipped)
{
next = edge_weight_tree->head;
continue;
} }
}
if(debug_lvl >= DEBUG_SCARY_THINGS)
syslog(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes, safe_edges);
} }
/* Implementation of a simple breadth-first search algorithm. /* Implementation of a simple breadth-first search algorithm.