Add graph references

references/SkienaBook/queue.c

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+// vim:fileencoding=utf-8:foldmethod=marker
+
+/*    queue.c
+
+    Implementation of a FIFO queue abstract 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 <stdbool.h>
+
+#include "queue.h"
+
+void init_queue(queue *q) {
+    q->first = 0;
+    q->last = QUEUESIZE - 1;
+    q->count = 0;
+}
+
+void enqueue(queue *q, item_type x) {
+    if (q->count >= QUEUESIZE) {
+        printf("Warning: queue overflow enqueue x=%d\n", x);
+    } else {
+        q->last = (q->last + 1) % QUEUESIZE;
+        q->q[q->last] = x;    
+        q->count = q->count + 1;
+    }
+}
+
+item_type dequeue(queue *q) {
+    item_type x;
+
+    if (q->count <= 0) printf("Warning: empty queue dequeue.\n");
+
+    x = q->q[q->first];
+    q->first = (q->first + 1) % QUEUESIZE;
+    q->count = q->count - 1;
+
+    return(x);
+}
+
+item_type headq(queue *q) {
+    return(q->q[q->first]);
+}
+
+int empty_queue(queue *q) {
+    if (q->count <= 0) {
+        return (true);
+    }
+    return (false);
+}
+
+void print_queue(queue *q) {
+    int i;
+
+    i = q->first; 
+        
+    while (i != q->last) {
+        printf("%d ", q->q[i]);
+        i = (i + 1) % QUEUESIZE;
+    }
+
+    printf("%2d ", q->q[i]);
+    printf("\n");
+}