环形队列

1. 将数组queue[mMaxSize]视为环，队列头指针front，尾指针rear，为了避免二义性，最多只容纳mMaxSize-1个元素；
2. front == rear时，队列为空；front == (rear+1) % mMaxSize时，队列为满；
3. front所指处不放元素；

4. void queueAdd(const int x) {
       int k = (rear + 1) % mMaxSize;
       if (front == k) 
           QueueFull();
       else {
           queue[k] = x;
           rear = k;
       } 
   }

   int  queueDelete() {
       if (front == rear) {
           QueueEmpty();
           return 0;
       }
       front = (front+1) % mMaxSize;
       return queue[front]; 
   }