#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
typedef int ElemType;

//链队列的结点定义 
typedef struct node{
  ElemType val;
  struct node* next;
}QueueNode;

//链队列的定义，包含队头指针和队尾指针 
typedef struct queue {
  QueueNode* front;
  QueueNode* rear;
}LinkedQueue;

//初始化队列 
LinkedQueue* initQueue() {
  LinkedQueue* queue = (LinkedQueue*)malloc(sizeof(LinkedQueue));
  queue->front = (QueueNode*)malloc(sizeof(QueueNode));
  queue->front->next = NULL;
  queue->rear = queue->front;
}

//元素入队 
void enQueue(LinkedQueue* queue, ElemType elem) {
  QueueNode* node = (QueueNode*)malloc(sizeof(QueueNode));
  node->val = elem;
  node->next = NULL;
  queue->rear->next = node;
  queue->rear = node;
}

//队列是否为空 
bool isQueueEmpty(LinkedQueue* queue) {
  return queue->front == queue->rear; 
}

//元素出队 
ElemType deQueue(LinkedQueue* queue) {
  if(!isQueueEmpty(queue)) {
    QueueNode* p = queue->front;
    queue->front = p->next;
    ElemType e = queue->front->val;
    free(p);
    return e;
  }
  return NULL;
}

int main()
{
  LinkedQueue* queue = initQueue();
  int i;
  for(i = 0; i < 20; i++) {
    enQueue(queue, i);
  }
  while(!isQueueEmpty(queue)) {
    printf("deQueue: %d\n", deQueue(queue));
  }
  return 0;
}