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+/* topsort.c (topological sorting of acyclic digraph) */
+
+/***********************************************************************
+* This code is part of GLPK (GNU Linear Programming Kit).
+*
+* Copyright (C) 2010-2016 Andrew Makhorin, Department for Applied
+* Informatics, Moscow Aviation Institute, Moscow, Russia. All rights
+* reserved. E-mail: <mao@gnu.org>.
+*
+* GLPK 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 3 of the License, or
+* (at your option) any later version.
+*
+* GLPK 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 GLPK. If not, see <http://www.gnu.org/licenses/>.
+***********************************************************************/
+
+#include "env.h"
+#include "glpk.h"
+
+/***********************************************************************
+* NAME
+*
+* glp_top_sort - topological sorting of acyclic digraph
+*
+* SYNOPSIS
+*
+* int glp_top_sort(glp_graph *G, int v_num);
+*
+* DESCRIPTION
+*
+* The routine glp_top_sort performs topological sorting of vertices of
+* the specified acyclic digraph.
+*
+* The parameter v_num specifies an offset of the field of type int in
+* the vertex data block, to which the routine stores the vertex number
+* assigned. If v_num < 0, vertex numbers are not stored.
+*
+* The vertices are numbered from 1 to n, where n is the total number
+* of vertices in the graph. The vertex numbering has the property that
+* for every arc (i->j) in the graph the condition num(i) < num(j)
+* holds. Special case num(i) = 0 means that vertex i is not assigned a
+* number, because the graph is *not* acyclic.
+*
+* RETURNS
+*
+* If the graph is acyclic and therefore all the vertices have been
+* assigned numbers, the routine glp_top_sort returns zero. Otherwise,
+* if the graph is not acyclic, the routine returns the number of
+* vertices which have not been numbered, i.e. for which num(i) = 0. */
+
+static int top_sort(glp_graph *G, int num[])
+{ glp_arc *a;
+ int i, j, cnt, top, *stack, *indeg;
+ /* allocate working arrays */
+ indeg = xcalloc(1+G->nv, sizeof(int));
+ stack = xcalloc(1+G->nv, sizeof(int));
+ /* determine initial indegree of each vertex; push into the stack
+ the vertices having zero indegree */
+ top = 0;
+ for (i = 1; i <= G->nv; i++)
+ { num[i] = indeg[i] = 0;
+ for (a = G->v[i]->in; a != NULL; a = a->h_next)
+ indeg[i]++;
+ if (indeg[i] == 0)
+ stack[++top] = i;
+ }
+ /* assign numbers to vertices in the sorted order */
+ cnt = 0;
+ while (top > 0)
+ { /* pull vertex i from the stack */
+ i = stack[top--];
+ /* it has zero indegree in the current graph */
+ xassert(indeg[i] == 0);
+ /* so assign it a next number */
+ xassert(num[i] == 0);
+ num[i] = ++cnt;
+ /* remove vertex i from the current graph, update indegree of
+ its adjacent vertices, and push into the stack new vertices
+ whose indegree becomes zero */
+ for (a = G->v[i]->out; a != NULL; a = a->t_next)
+ { j = a->head->i;
+ /* there exists arc (i->j) in the graph */
+ xassert(indeg[j] > 0);
+ indeg[j]--;
+ if (indeg[j] == 0)
+ stack[++top] = j;
+ }
+ }
+ /* free working arrays */
+ xfree(indeg);
+ xfree(stack);
+ return G->nv - cnt;
+}
+
+int glp_top_sort(glp_graph *G, int v_num)
+{ glp_vertex *v;
+ int i, cnt, *num;
+ if (v_num >= 0 && v_num > G->v_size - (int)sizeof(int))
+ xerror("glp_top_sort: v_num = %d; invalid offset\n", v_num);
+ if (G->nv == 0)
+ { cnt = 0;
+ goto done;
+ }
+ num = xcalloc(1+G->nv, sizeof(int));
+ cnt = top_sort(G, num);
+ if (v_num >= 0)
+ { for (i = 1; i <= G->nv; i++)
+ { v = G->v[i];
+ memcpy((char *)v->data + v_num, &num[i], sizeof(int));
+ }
+ }
+ xfree(num);
+done: return cnt;
+}
+
+/* eof */