From 6dcb6d6c6d10c565baf61e6d2ef1588d29aa263f Mon Sep 17 00:00:00 2001
From: Wei Yang <richard.weiyang@gmail.com>
Date: Wed, 10 Oct 2018 15:47:24 +0800
Subject: [PATCH] implement ring queue in c

---
 c-cpp/09_queue/ring_queue.c | 130 ++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 c-cpp/09_queue/ring_queue.c

diff --git a/c-cpp/09_queue/ring_queue.c b/c-cpp/09_queue/ring_queue.c
new file mode 100644
index 00000000..1ae29f00
--- /dev/null
+++ b/c-cpp/09_queue/ring_queue.c
@@ -0,0 +1,130 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+struct ring_queue {
+	int cap;
+	int head, tail;
+	int *_q;
+};
+
+int alloc_queue(struct ring_queue* queue, int cap)
+{
+	if (!queue || cap < 0)
+		return -1;
+	if (queue->_q)
+		return -1;
+
+	queue->_q = (int *)malloc(cap * sizeof(int));
+	if (!queue->_q)
+		return -1;
+
+	queue->head = queue->tail = 0;
+	queue->cap = cap;
+	return 0;
+}
+
+void free_queue(struct ring_queue *queue)
+{
+	queue->cap = 0;
+	queue->head = queue->tail = 0;
+	free(queue->_q);
+}
+
+int _valid_index(int curr, int step, int cap)
+{
+	return (curr + step) % cap;
+}
+
+int _next(int curr, int cap)
+{
+	return _valid_index(curr, 1, cap);
+}
+
+bool is_empty(struct ring_queue *queue)
+{
+	return (queue->head == queue->tail);
+}
+
+bool is_full(struct ring_queue *queue)
+{
+	int next_tail = _next(queue->tail, queue->cap);
+	return (next_tail == queue->head);
+}
+
+int enqueue(struct ring_queue* queue, int elem)
+{
+	if (is_full(queue))
+		return -1;
+
+	queue->_q[queue->tail] = elem;
+	queue->tail = _next(queue->tail, queue->cap);
+	return 0;
+}
+
+int dequeue(struct ring_queue* queue, int *elem)
+{
+	if (is_empty(queue))
+		return -1;
+
+	if (elem)
+		*elem = queue->_q[queue->head];
+	queue->head = _next(queue->head, queue->cap);
+	return 0;
+}
+
+int size(struct ring_queue* queue)
+{
+	int size = queue->tail - queue->head;
+
+	if (size < 0)
+		size += queue->cap;
+	return size;
+}
+
+void dump(struct ring_queue* queue)
+{
+	int i, idx;
+
+	printf("Queue has %d elements with %d capacity\n",
+		size(queue), queue->cap);
+	for (i = 0; i < size(queue); i++) {
+		idx = _valid_index(queue->head, i, queue->cap);
+		printf("[%02d]: %08d\n", idx, queue->_q[idx]);
+	}
+}
+
+int main()
+{
+	struct ring_queue queue = {0, 0, 0, NULL};
+	int i;
+
+	if (alloc_queue(&queue, 8)) {
+		printf("Failed to allocate a queue\n");
+		return -1;
+	}
+
+	printf("A new queue is %s\n", is_empty(&queue)?"empty":"not empty");
+
+	enqueue(&queue, 1);
+	printf("After enqueue 1 element, queue is %s\n", is_empty(&queue)?"empty":"not empty");
+	dequeue(&queue, NULL);
+	printf("After dequeue 1 element, queue is %s\n", is_empty(&queue)?"empty":"not empty");
+
+	for (i = 0; i < 7; i++)
+		enqueue(&queue, i);
+	printf("After enqueue 7 element, queue is %s\n", is_full(&queue)?"full":"not full");
+
+	for (i = 0; i < 4; i++) {
+		dequeue(&queue, NULL);
+		enqueue(&queue, i);
+	}
+	printf("After enqueue/dequeue 4 element, queue is %s\n",
+			is_full(&queue)?"full":"not full");
+	printf("Head is %d, Tail is %d\n", queue.head, queue.tail);
+
+	dump(&queue);
+	free_queue(&queue);
+	return 0;
+}