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;
}