隊(duì)列也可以數(shù)組和鏈表的結(jié)構(gòu)實(shí)現(xiàn)，使用鏈表的結(jié)構(gòu)實(shí)現(xiàn)更優(yōu)一些，因?yàn)槿绻褂脭?shù)組的結(jié)構(gòu)，出隊(duì)列在數(shù)組頭上出數(shù)據(jù)，效率會(huì)比較低，時(shí)間復(fù)雜度為O(n)。

2.?；静僮鞯膶?shí)現(xiàn)

2.1 初始化棧

void StackInit(stack*ps)
{
	assert(ps);
	ps->_a = (StackDate*)malloc(sizeof(StackDate) * 4);
	ps->_top = 0;
	ps->_capacity = 4;
}

2.2 入棧

void StackPush(stack*ps, StackDate x)
{
	assert(ps);
	if (ps->_top == ps->_capacity)
	{
		stack*tmp = (StackDate*)realloc(ps, sizeof(StackDate)*(ps->_capacity) * 2);
		if (NULL == tmp)
		{
			printf("realloc failed\n");
			exit(-1);
		}
		ps = tmp;
		ps->_capacity *= 2;
	}
	ps->_a[ps->_top] = x;
	ps->_top++;
}

2.3 出棧

void StackPop(stack*ps)
{
	assert(ps);
	assert(!StackIsEmpty(ps));
	--ps->_top;
}

注意：出棧并不是真正意義上的刪除數(shù)據(jù)，而是將_top向后挪動(dòng)了一個(gè)位置。

2.4 獲取棧頂數(shù)據(jù)

StackDate StackTop(stack*ps)
{
	assert(ps);
	assert(!StackIsEmpty(ps));
	return ps->_a[ps->_top - 1];
}

2.5 獲取棧中有效元素個(gè)數(shù)

int StackSize(stack*ps)
{
	assert(ps);
	return ps->_top;
}

2.6 判斷棧是否為空

bool StackIsEmpty(stack*ps)
{
	assert(ps);
	return ps->_top == 0;
}

2.7 銷毀棧

void StackDestory(stack*ps)
{
	assert(ps);
	free(ps->_a);
	ps->_a = NULL;
	ps->_top = ps->_capacity = 0;
}

3.測(cè)試

3.1 測(cè)試

void test()
{
	//插入數(shù)據(jù)
	stack  st;
	StackInit(&st);
	StackPush(&st,1);
	StackPush(&st,2);
	StackPush(&st,3);
	StackPush(&st,4);
	while (!StackIsEmpty(&st))
	{
		printf("%d ", StackTop(&st));
		StackPop(&st);
	}
	printf("\n");


	//獲取棧頂數(shù)據(jù)
	StackPush(&st, 1);
	StackPush(&st, 2);
	printf("%d ", StackTop(&st));
	printf("\n");

	
	//棧中有效數(shù)據(jù)個(gè)數(shù)
	printf("%d ", StackSize(&st));

	
	//銷毀棧
	StackDestory(&st);
}

3.2 測(cè)試結(jié)果

4.思考-2

為什么隊(duì)列用鏈表模擬比數(shù)組模擬更加合適？

棧的實(shí)現(xiàn)一般可以使用數(shù)組或者鏈表實(shí)現(xiàn)，相對(duì)而言數(shù)組的結(jié)構(gòu)實(shí)現(xiàn)更優(yōu)一些。因?yàn)閿?shù)組在尾上插入數(shù)據(jù)的代價(jià)小。

5.隊(duì)列的基本操作實(shí)現(xiàn)

5.1 初始化隊(duì)列

void QueueInit(Queue*pq)
{
	assert(pq);
	pq->_head = pq->_tail = NULL;
}

5.2 隊(duì)尾入隊(duì)列

void QueuePush(Queue*pq, QueueDate x)
{
	assert(pq);
	QueueNode*newnode = (QueueNode*)malloc(sizeof(QueueNode));
	if (NULL == newnode)
	{
		printf("malloc failed\n");
		exit(-1);
	}
	newnode->next = NULL;
	newnode->val = x;
	if (NULL == pq->_tail)
	{
		pq->_head = pq->_tail = newnode;
	}
	else
	{
		pq->_tail->next = newnode;
		pq->_tail = newnode;
	}
}

5.3 隊(duì)頭出隊(duì)列

void QueuePop(Queue*pq)
{
	assert(pq);
	assert(!QueueIsEmpty(pq));
	if (NULL == pq->_head->next)
	{
		free(pq->_head);
		pq->_head = pq->_tail = NULL;
		
	}
	else
	{
		QueueNode*next = pq->_head->next;
		free(pq->_head);
		pq->_head = next;
	}
}

代碼分析：

5.4 隊(duì)列中有效元素的個(gè)數(shù)

int QueueSize(Queue*pq)
{
	assert(pq);
	int count = 0;
	QueueNode*cur = pq->_head;
	while (cur)
	{
		++count;
		cur = cur->next;
	}
	return count;
}

5.5 判斷隊(duì)列是否為空

bool QueueIsEmpty(Queue*pq)
{
	assert(pq);
	return pq->_head == NULL;
}

5.6 獲取隊(duì)頭數(shù)據(jù)

QueueDate QueueFront(Queue*pq)
{
	assert(pq);
	assert(!QueueIsEmpty(pq));
	return pq->_head->val;
}

5.7 獲取隊(duì)尾的數(shù)據(jù)

QueueDate QueueBack(Queue*pq)
{
	assert(pq);
	assert(!QueueIsEmpty(pq));
	return pq->_tail->val;
}

5.8 銷毀隊(duì)列

void QueueDestory(Queue*pq)
{
	assert(pq);
	while (pq->_head)
	{
		if (pq->_head == pq->_tail)
		{
			free(pq->_head);
			pq->_head = pq->_tail = NULL;
		}
		else
		{
			QueueNode*next = pq->_head->next;
			free(pq->_head);
			pq->_head = next;
		}
	}
}

注意：和隊(duì)頭出隊(duì)列一樣分析。

6.測(cè)試

6.1 測(cè)試

void test1()
{
	//插入數(shù)據(jù)
	Queue q;
	QueueInit(&q);
	QueuePush(&q, 1);
	QueuePush(&q, 2);
	QueuePush(&q, 3);
	QueuePush(&q, 4);


	//有效數(shù)據(jù)的個(gè)數(shù)
	printf("%d ", QueueSize(&q));
	printf("\n");


	//獲取隊(duì)頭數(shù)據(jù)
	printf("%d",QueueFront(&q));
	printf("\n");


	//獲取隊(duì)尾數(shù)據(jù)
	printf("%d",QueueBack(&q));
	printf("\n");


	//出隊(duì)
	QueuePop(&q);
	while (!QueueIsEmpty(&q))
	{
		printf("%d ", QueueFront(&q));
		QueuePop(&q);
	}
	printf("\n");


	//銷毀
	QueueDestory(&q);
	printf("\n");
}