算法导论-------------队列（queue）的简单实现

队列的基本操作包括入队enqueue和出队dequeue，队列有队头head和队尾tail指针。元素总是从队头出，从队尾入。采用数组实现队列时候，为了合理利用空间，可以采用循环实现队列空间的有效利用。

#include<iostream>
using namespace std;

struct queue
{
	int *q;
	int queuesize;
	int head;
	int tail;
};

void init(queue* q, int n)
{
	q->head = 0;
	q->tail = 0;
	q->queuesize = n;
	q->q = (int*)malloc(sizeof(int)*q->queuesize);
}

void enqueue(queue* q, int x)
{
	if (((q->tail + 1) % q->queuesize) == q->head)
	{
		cout << "queue is full" << endl;
	}
	else
	{
		q->q[q->tail] = x;
		q->tail = (q->tail + 1) % q->queuesize;
	}
}

int dequeue(queue* q, int *value)
{
	if (q->tail == q->head)
		return -1;
	else
	{
		*value = q->q[q->head];
		q->head = ((q->head++) % q->queuesize);
	}
}

int main()
{

	int value;
	queue q;
	init(&q, 10);

	for (int i = 0; i < 9; i++)
	{
		enqueue(&q, i + 11);
	}

	cout << "head=" << q.head << endl;
	cout << "tail=" << q.tail << endl;

	for (int i = 0; i < 9; i++)
	{
		if (dequeue(&q, &value) == -1)
			cout << "queque is empy"<<endl;
		else
			printf("value=%d\n", value);
	}

	cout << "head=" << q.head << endl;
	cout << "tail=" << q.tail << endl;

	return 0;
}