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/*!
\file lib/vector/neta/bridge.c
\brief Network Analysis library - bridges
Computes number of bridges in the graph.
(C) 2009-2010 by Daniel Bundala, and the GRASS Development Team
This program is free software under the GNU General Public License
(>=v2). Read the file COPYING that comes with GRASS for details.
\author Daniel Bundala (Google Summer of Code 2009)
*/
#include <stdio.h>
#include <stdlib.h>
#include <grass/gis.h>
#include <grass/vector.h>
#include <grass/glocale.h>
#include <grass/dgl/graph.h>
/*!
\brief Get number of bridges in the graph.
Bridge is an array containing the indices of the bridges.
\param graph input graph
\param[out] bridge_list list of bridges
\return number of bridges, -1 on error
*/
int NetA_compute_bridges(dglGraph_s *graph, struct ilist *bridge_list)
{
int nnodes;
int bridges = 0;
dglEdgesetTraverser_s
*current; /*edge to be processed when the node is visited */
int *tin, *min_tin; /*time in, and smallest tin over all successors. 0 if
not yet visited */
dglInt32_t *parent; /*edge from parent to the node */
dglInt32_t **stack; /*stack of nodes */
dglInt32_t **current_edge; /*current edge for each node */
dglNodeTraverser_s nt;
dglInt32_t *current_node;
int stack_size;
int i, time;
nnodes = dglGet_NodeCount(graph);
current = (dglEdgesetTraverser_s *)G_calloc(nnodes + 1,
sizeof(dglEdgesetTraverser_s));
tin = (int *)G_calloc(nnodes + 1, sizeof(int));
min_tin = (int *)G_calloc(nnodes + 1, sizeof(int));
parent = (dglInt32_t *)G_calloc(nnodes + 1, sizeof(dglInt32_t));
stack = (dglInt32_t **)G_calloc(nnodes + 1, sizeof(dglInt32_t *));
current_edge = (dglInt32_t **)G_calloc(nnodes + 1, sizeof(dglInt32_t *));
if (!tin || !min_tin || !parent || !stack || !current) {
G_fatal_error(_("Out of memory"));
return -1;
}
for (i = 1; i <= nnodes; i++) {
dglEdgeset_T_Initialize(
¤t[i], graph,
dglNodeGet_OutEdgeset(graph, dglGetNode(graph, i)));
current_edge[i] = dglEdgeset_T_First(¤t[i]);
tin[i] = 0;
}
dglNode_T_Initialize(&nt, graph);
time = 0;
for (current_node = dglNode_T_First(&nt); current_node;
current_node = dglNode_T_Next(&nt)) {
dglInt32_t current_id = dglNodeGet_Id(graph, current_node);
if (tin[current_id] == 0) {
stack[0] = current_node;
stack_size = 1;
parent[current_id] = 0;
while (stack_size) {
dglInt32_t *node = stack[stack_size - 1];
dglInt32_t node_id = dglNodeGet_Id(graph, node);
if (tin[node_id] == 0) /*vertex visited for the first time */
min_tin[node_id] = tin[node_id] = ++time;
else { /*return from the recursion */
dglInt32_t to = dglNodeGet_Id(
graph, dglEdgeGet_Tail(graph, current_edge[node_id]));
if (min_tin[to] >
tin[node_id]) { /*no path from the subtree above the
current node */
Vect_list_append(
bridge_list,
dglEdgeGet_Id(
graph, current_edge[node_id])); /*so it must be
a bridge */
bridges++;
}
if (min_tin[to] < min_tin[node_id])
min_tin[node_id] = min_tin[to];
current_edge[node_id] = dglEdgeset_T_Next(
¤t[node_id]); /*proceed to the next edge */
}
for (; current_edge[node_id];
current_edge[node_id] = dglEdgeset_T_Next(
¤t[node_id])) { /*try next edges */
dglInt32_t *to =
dglEdgeGet_Tail(graph, current_edge[node_id]);
dglInt32_t edge_id =
dglEdgeGet_Id(graph, current_edge[node_id]);
if (labs(edge_id) == parent[node_id])
continue; /*skip edge we used to travel to this node */
int to_id = dglNodeGet_Id(graph, to);
if (tin[to_id]) { /*back edge, cannot be a
bridge/articualtion point */
if (tin[to_id] < min_tin[node_id])
min_tin[node_id] = tin[to_id];
}
else { /*forward edge */
parent[to_id] = labs(edge_id);
stack[stack_size++] = to;
break;
}
}
if (!current_edge[node_id])
stack_size--; /*current node completely processed */
}
}
}
dglNode_T_Release(&nt);
for (i = 1; i <= nnodes; i++)
dglEdgeset_T_Release(¤t[i]);
G_free(current);
G_free(tin);
G_free(min_tin);
G_free(parent);
G_free(stack);
G_free(current_edge);
return bridges;
}
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