/* topsort1.c Topologically sort a directed acyclic graph by DFS numbering (DAG) */ /* Copyright 2003-2020 by Steven S. Skiena; all rights reserved. Permission is granted for use in non-commerical applications provided this copyright notice remains intact and unchanged. These programs appear in my books: "The Algorithm Design Manual" by Steven Skiena, second edition, Springer, London 2008. See out website www.algorist.com for additional information or https://www.amazon.com/exec/obidos/ASIN/1848000693/thealgorith01-20 "Programming Challenges: The Programming Contest Training Manual" by Steven Skiena and Miguel Revilla, Springer-Verlag, New York 2003. See our website www.programming-challenges.com for additional information, or https://www.amazon.com/exec/obidos/ASIN/0387001638/thealgorithmrepo/ */ #include #include #include "bfs-dfs.h" #include "stack.h" stack sorted; /* topological ordering of vertices */ extern bool processed[]; /* which vertices have been processed */ extern bool discovered[]; /* which vertices have been found */ extern int parent[]; /* discovery relation */ extern int entry_time[]; /* time of vertex entry */ extern int exit_time[]; /* time of vertex exit */ void process_vertex_early(int v) { } /* [[[ pvlate_topsort_cut */ void process_vertex_late(int v) { push(&sorted, v); } /* ]]] */ /* [[[ pedge_topsort_cut */ void process_edge(int x, int y) { int class; /* edge class */ class = edge_classification(x, y); if (class == BACK) { printf("Warning: directed cycle found, not a DAG\n"); } } /* ]]] */ /* [[[ topsort_cut */ void topsort(graph *g) { int i; /* counter */ init_stack(&sorted); for (i = 1; i <= g->nvertices; i++) { if (!discovered[i]) { dfs(g, i); } } print_stack(&sorted); /* report topological order */ } /* ]]] */ int main(void) { graph g; read_graph(&g, true); print_graph(&g); topsort(&g); return 0; }