Function enqueue

contents/tree_traversal/code/c/utility.h:83–90

}

void enqueue(struct queue *q, void *element) {
    if (q->front == (q->back + 1) % q->capacity) {
        queue_resize(q);
    }

    q->data[q->back] = element;
    q->back = (q->back + 1) % q->capacity;
}

void *dequeue(struct queue *q) {
    if (queue_empty(q)) {