/* bipartite.c Two color a bipartite graph */ /* 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 http://www.amazon.com/exec/obidos/ASIN/0387001638/thealgorithmrepo/ */ #include #include #include "bfs-dfs.h" #include "queue.h" 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[MAXV+1]; /* time of vertex entry */ extern int exit_time[MAXV+1]; /* time of vertex exit */ #define UNCOLORED 0 /* vertex not yet colored */ #define WHITE 1 /* white vertex */ #define BLACK 2 /* black vertex */ int color[MAXV+1]; /* assigned color of v */ bool bipartite; /* is the graph bipartite? */ void process_vertex_early(int v) { } void process_vertex_late(int v) { } /* [[[ complement_cut */ int complement(int color) { if (color == WHITE) { return(BLACK); } if (color == BLACK) { return(WHITE); } return(UNCOLORED); } /* ]]] */ /* [[[ pecolor_cut */ void process_edge(int x, int y) { if (color[x] == color[y]) { bipartite = false; printf("Warning: not bipartite, due to (%d,%d)\n", x, y); } color[y] = complement(color[x]); } /* ]]] */ /* [[[ twocolor_cut */ void twocolor(graph *g) { int i; /* counter */ for (i = 1; i <= (g->nvertices); i++) { color[i] = UNCOLORED; } bipartite = true; initialize_search(g); for (i = 1; i <= (g->nvertices); i++) { if (!discovered[i]) { color[i] = WHITE; bfs(g, i); } } } /* ]]] */ int main(void) { graph g; int i; read_graph(&g, false); print_graph(&g); twocolor(&g); for (i = 1; i <= (g.nvertices); i++) { printf(" %d", color[i]); } printf("\n"); return 0; }