循环队列 EMPTY QUEUE How to test when queue is empty? [2] [3] [2] [3] [1] [4] [1] [4] [0] [5] [0] [5] front = 0 front = 0 rear = 0 rear = 3 J2 J1 J3 循环队列 How to test when queue is full? [2] [3] [2] [3] [1