/* findcycle.c Identify a cycle in a graph, if one exists. */ /* 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" extern bool processed[]; /* which vertices have been processed */ extern bool discovered[]; /* which vertices have been found */ extern int parent[]; /* discovery relation */ extern bool finished; /* flag for early search cutoff */ void process_vertex_early(int v) { } void process_vertex_late(int v) { } /* [[[ cyclepedge_cut */ void process_edge(int x, int y) { if (parent[y] != x) { /* found back edge! */ printf("Cycle from %d to %d:", y, x); find_path(y, x, parent); finished = true; } } /* ]]] */ int main(void) { graph g; read_graph(&g, false); print_graph(&g); initialize_search(&g); dfs(&g, 1); printf("\n"); return 0; }