循环队列的实现

循环队列是一种线性数据结构，其操作表现基于 FIFO（先进先出）原则并且队尾被连接在队首之后以形成一个循环。它也被称为“环形缓冲器”。

循环队列的一个好处是我们可以利用这个队列之前用过的空间。在一个普通队列里，一旦一个队列满了，我们就不能插入下一个元素，即使在队列前面仍有空间。但是使用循环队列，我们能使用这些空间去存储新的值。

/**
 * 循环队列
 */
public class MyCircularQueue {
    public int[] data;
    public int capacity;
    public int p_tail;
    public int p_head;
    public boolean firstAdd =true;
    /** Initialize your data structure here. Set the size of the queue to be k. */
    public MyCircularQueue(int k) {
        data = new int[k];
        capacity = 0;
        p_tail = -1;
        p_head = -1;

    }

    /** Insert an element into the circular queue. Return true if the operation is successful. */
    public boolean enQueue(int value) {
        if(isFull()){
            return false;
        }
        if(firstAdd){
            p_head = 0;
            p_tail = 0;
            firstAdd = false;
        }else{
            if(p_tail == data.length-1){
                p_tail = 0;
            }else{
                p_tail++;
            }
        }

        data[p_tail]=value;
        capacity++;
        return true;

    }

    /** Delete an element from the circular queue. Return true if the operation is successful. */
    public boolean deQueue() {
        if(isEmpty()){
            return false;
        }
        if(p_head == data.length-1){
            p_head = 0;
        }else{
            p_head++;
        }
        capacity--;
        return true;
    }

    /** Get the front item from the queue. */
    public int Front() {

        if(isEmpty()){
            return -1;
        }

        return data[p_head];
    }

    /** Get the last item from the queue. */
    public int Rear() {
        if(isEmpty()){
            return -1;
        }
        return data[p_tail];
    }

    /** Checks whether the circular queue is empty or not. */
    public boolean isEmpty() {
        return capacity == 0;
    }

    /** Checks whether the circular queue is full or not. */
    public boolean isFull() {

        return capacity == data.length;

    }

    public static void main(String[] args) {
        MyCircularQueue circularQueue = new MyCircularQueue(2); // 设置长度为 2

        System.out.println(circularQueue.enQueue(4));
        System.out.println(circularQueue.Rear());
        System.out.println(circularQueue.enQueue(9));
        System.out.println(circularQueue.deQueue());
        System.out.println(circularQueue.Front());


//        System.out.println(circularQueue.Front());
//        System.out.println(circularQueue.deQueue());
//        System.out.println( circularQueue.Front());
//        System.out.println(circularQueue.deQueue());
//        System.out.println(circularQueue.Front());
//        System.out.println(circularQueue.enQueue(4));
//        System.out.println(circularQueue.enQueue(2));
//        System.out.println(circularQueue.enQueue(2));
//        System.out.println(circularQueue.enQueue(3));
    }
}