数据结构-循环队列

1.代码

#include <stdio.h>
#include <malloc.h>

#define TOTAL_SPACE 5

/**
 * Circle int queue.
 */
typedef struct CircleIntQueue{
	int data[TOTAL_SPACE];
	int front;
	int rear;
}*CircleIntQueuePtr;

/**
 * Initialize the queue.
 */
CircleIntQueuePtr initQueue() {
	CircleIntQueuePtr resultPtr = (CircleIntQueuePtr)malloc(sizeof(struct CircleIntQueue));
	resultPtr->front = 0;
	resultPtr->rear = 0;

	return resultPtr;
}// Of the first constructor

/**
 * Enqueue.
 * 
 * @param paraValue The value of the new node.
 */
void enqueue(CircleIntQueuePtr paraPtr, int paraValue) {
	printf("Enqueue: %d ", paraValue);
	if ((paraPtr->rear + 1) % TOTAL_SPACE == paraPtr->front) {
		printf("Queue full.\r\n");
		return;
	} // Of if

	paraPtr->data[paraPtr->rear] = paraValue;
	paraPtr->rear = (paraPtr->rear + 1) % TOTAL_SPACE;
}// Of enqueue

/**
 * Dequeue.
 * @return The value at the front.
 */
int dequeue(CircleIntQueuePtr paraPtr) {
	int resultValue;
	if (paraPtr->front == paraPtr->rear) {
		printf("No element in the queue.\r\n");
		return -1;
	} // Of if

	resultValue = paraPtr->data[paraPtr->front];
	paraPtr->front = (paraPtr->front + 1) % TOTAL_SPACE;

	return resultValue;
}// Of dequeue

/**
 * Output the queue.
 */
void outputCircleIntQueue(CircleIntQueuePtr paraPtr){
	int i;
	if (paraPtr->front == paraPtr->rear) {
		printf("Empty queue.");
		return;
	} // Of if

	printf("Elements in the queue: ");
	for (i = paraPtr->front; i != paraPtr->rear; i = (i + 1) % TOTAL_SPACE) {
		printf("data[%d] = %d, ", i, paraPtr->data[i]);
	} // Of for i

	printf("\r\n");
}//Of outputCircleIntQueue

/**
 * Unit test.
 */
void testCircleIntQueue(){
	int i = 10;
	CircleIntQueuePtr tempPtr = initQueue();
	for (; i < 16; i ++) {
		enqueue(tempPtr, i);
	}//Of for i

	outputCircleIntQueue(tempPtr);

	for (i = 0; i < 6; i ++) {
		printf("dequeue gets %d\r\n", dequeue(tempPtr));
	}//Of for i

	for (i = 3; i < 6; i ++) {
		enqueue(tempPtr, i);
	}//Of for i
	for (i = 20; i < 30; i ++) {
		enqueue(tempPtr, i);
		printf("dequeue gets %d\r\n", dequeue(tempPtr));
		outputCircleIntQueue(tempPtr);
	}//Of for i
}//Of testCircleIntQueue

/**
 * The entrance.
 */
int main(){
	testCircleIntQueue();
	return 1;
}//Of main

2.理解

假溢出：

如果 rear++ :

那么结果如图d，队列出现“上溢出”，然而却又不是真正的溢出，所以是一种“假溢出”。就是空间还没有被占满，尾指针rear就超出内存的最大值。

解决办法： rear = （ rear + 1）/  TOTAL_SPACE ；那么图d就成为了图e：

第二个特别重要的点：

出队时：front = （ front + 1 ）/ TOTAL_SPACE ；

如果图e是 front++ ：

那么front就会溢出，而队列为空；所以当 front = （ front + 1 ）/ TOTAL_SPACE 时， front == rear ，判断出队列为空。