队列的数组实现

数据结构与算法分析——c语言描述 第三章  队列的数组实现

注意rear和front初始化的赋值。

queue.h

typedef int ElementType;

#ifndef _Queue_h
#define _Queue_h

struct QueueRecord;
typedef struct QueueRecord *Queue;

int isEmpty(Queue q);
int isFull(Queue q);
Queue createQueue(int maxElements);
void disposeQueue(Queue q);
void makeEmpty(Queue q);
void enqueue(ElementType X, Queue q);
ElementType front(Queue q);
void dequeue(Queue q);
ElementType frontAndDequeue(Queue q);

#endif  

queue.c

#include"queue.h"
#include"fatal.h"
#include<stdlib.h>

#define	MinQueueSize (5)

struct QueueRecord{
	int capacity;
	int front;
	int rear;
	int size;
	ElementType *array;
};



int isEmpty(Queue q) {
	return q->size == 0;
}

int isFull(Queue q) {
	return q->size == q->capacity;
}

Queue createQueue(int maxElements) {
	if (maxElements < MinQueueSize)
		Error("Queue size is too small");
	Queue q = malloc(sizeof(struct QueueRecord));
	if (q == NULL)
		Error("out of memory");
	q->array = malloc(maxElements*sizeof(ElementType));
	if(q->array==NULL)
		Error("out of memory");
	q->capacity = maxElements;
	makeEmpty(q);
	return q;
}

void makeEmpty(Queue q) {
	q->size = 0;
	q->front = 1;//这个是重点啊，当增加一个元素之后，rear和front同时都是1
	q->rear = 0;
}

void enqueue(ElementType X, Queue q) {
	if (isFull(q))
		Error("queue is full");
	q->size++;
	q->rear = (q->rear + 1) % q->capacity;
	q->array[q->rear] = X;
}

ElementType front(Queue q) {
	if (isEmpty(q))
		Error("queue is empty");
	return q->array[q->front];
}

void dequeue(Queue q) {
	if (isEmpty(q))
		Error("queue is empty");
	q->size--;
	q->front = (q->front + 1) % q->capacity;
}

ElementType frontAndDequeue(Queue q) {
	ElementType x = front(q);
	dequeue(q);
	return x;
}

main.c

#include<stdlib.h>
#include<stdio.h>
#include"queue.h"

int main() {
	Queue q = createQueue(50);
	for (int i = 0; i < 8; i++){
		enqueue(i, q);
	}
	printf("%d\n", frontAndDequeue(q));
	printf("%d\n", frontAndDequeue(q));
	printf("%d\n", frontAndDequeue(q));
}