Add graph references

references/SkienaBook/graph.c

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+// vim:fileencoding=utf-8:foldmethod=marker
+
+/*	graph.c         
+
+	A generic adjacency list graph data type.
+*/
+
+/* 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 <stdio.h>
+#include <stdlib.h>
+
+#include "queue.h"
+#include "graph.h"
+
+/* [[[ init_graph_c */
+void initialize_graph(graph *g, bool directed) {
+    int i;    /* counter */
+
+    g->nvertices = 0;
+    g->nedges = 0;
+    g->directed = directed;
+
+    for (i = 1; i <= MAXV; i++) {
+        g->degree[i] = 0;
+    }
+
+    for (i = 1; i <= MAXV; i++) {
+        g->edges[i] = NULL;
+    }
+}
+/* ]]] */
+
+/* [[[ insert_edge_cut */
+void insert_edge(graph *g, int x, int y, bool directed) {
+    edgenode *p;        /* temporary pointer */
+
+    p = malloc(sizeof(edgenode));    /* allocate edgenode storage */
+
+    p->weight = 0;
+    p->y = y;
+    p->next = g->edges[x];
+
+    g->edges[x] = p;    /* insert at head of list */
+
+    g->degree[x]++;
+
+    if (!directed) {
+        insert_edge(g, y, x, true);
+    } else {
+        g->nedges++;
+    }
+}
+/* ]]] */
+
+/* [[[ read_graph_cut */
+void read_graph(graph *g, bool directed) {
+    int i;              /* counter */
+    int m;              /* number of edges */
+    int x, y;           /* vertices in edge (x,y) */
+
+    initialize_graph(g, directed);
+
+    scanf("%d %d", &(g->nvertices), &m);
+
+    for (i = 1; i <= m; i++) {
+        scanf("%d %d", &x, &y);
+        insert_edge(g, x, y, directed);
+    }
+}
+/* ]]] */
+
+void delete_edge(graph *g, int x, int y, bool directed) {
+    edgenode *p, *p_back; /* temporary pointers */
+
+    p = g->edges[x];
+    p_back = NULL;
+
+    while (p != NULL) {
+        if (p->y == y) {
+            g->degree[x]--;
+            if (p_back != NULL) {
+                p_back->next = p->next;
+            } else {
+                g->edges[x] = p->next;
+            }
+            free(p);
+            if (!directed) {
+                delete_edge(g, y, x, true);
+            } else {
+                g->nedges--;
+            }
+            return;
+        } else {
+            p = p->next;
+        }
+    }
+    printf("Warning: deletion(%d,%d) not found in g.\n",x,y);
+}
+
+/* [[[ print_graph_cut */
+void print_graph(graph *g) {
+    int i;        /* counter */
+    edgenode *p;  /* temporary pointer */
+
+    for (i = 1; i <= g->nvertices; i++) {
+        printf("%d: ", i);
+        p = g->edges[i];
+        while (p != NULL) {
+            printf(" %d", p->y);
+            p = p->next;
+        }
+        printf("\n");
+    }
+}
+/* ]]] */
+
+/* [[[ graph_transpose_cut */
+graph *transpose(graph *g) {
+    graph *gt;    /* transpose of graph g */
+    int x;        /* counter */
+    edgenode *p;  /* temporary pointer */
+
+    gt = (graph *) malloc(sizeof(graph));
+    initialize_graph(gt, true);       /* initialize directed graph */
+    gt->nvertices = g->nvertices;
+
+    for (x = 1; x <= g->nvertices; x++) {
+        p = g->edges[x];
+        while (p != NULL) {
+            insert_edge(gt, p->y, x, true);
+            p = p->next;
+        }
+    }
+
+    return(gt);
+}
+/* ]]] */