数据结构与算法学习（2)

环形队列

public class 循环队列 {
    //当队列满时，(rear+1)%maxSize == front;
    //队列空的时候，rear==front；
    //数组有效的元素个数 (rear-front+maxSize)%maxSize;
    public static void main(String[] args) {
        CircleArray array = new CircleArray(5);
        char key = ' ';
        Scanner scanner = new Scanner(System.in);
        boolean loop = true;
        while (loop) {
            System.out.println("s：显示队列");
            System.out.println("e：退出");
            System.out.println("a：添加");
            System.out.println("g：取出数据");
            System.out.println("p：查看队列头");
            System.out.println("q：查看多少个元素");
            key = scanner.next().charAt(0);
            switch (key) {
                case 's':
                    array.showQueue();
                    break;
                case 'a':
                    System.out.println("输入一个数字：");
                    int value = scanner.nextInt();
                    array.addQueue(value);
                    break;
                case 'g':
                    try {
                        int queue = array.getQueue();
                        System.out.println(queue);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'p':
                    try {
                        int i = array.peekQueue();
                        System.out.println(i);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'q':
                    System.out.println(array.size());
                    break;
                case 'e':
                    scanner.close();
                    loop = false;
                default:
                    break;
            }
        }
        System.out.println("程序退出!");
    }


}

//写一个类
class CircleArray {
    private int maxSize;
    //front指向第一个元素
    private int front;
    //rear指向队列的预留空间
    private int rear;
    private int[] arr;//存放数据

    public CircleArray(int maxSize) {
        this.maxSize = maxSize;
        arr = new int[maxSize];
        front = 0;
        rear = 0; //指向队列头部
    }

    public boolean isFull() {
        return ((rear + 1) % maxSize == front);
    }

    public boolean isEmpty() {
        return (rear == front);
    }

    public void addQueue(int n) {
        if (isFull()) {
            System.out.println("队列已满");
            return;
        }
        arr[rear] = n;
        //将rear后移 因为rear可能循环到了原本的队头 所以取模运算
        rear = (rear + 1) % maxSize;
    }

    public int getQueue() {
        if (isEmpty()) {
            throw new RuntimeException("队列空");
        }
        //先把front指向的值先取出来，再后移
        int value = arr[front];
        front = (front + 1) % maxSize;
        return value;
    }

    //  求出当前数据有效个数
    public int size() {
        return (rear - front + maxSize) % maxSize;
    }

    public void showQueue() {
        if (isEmpty()) {
            System.out.println("队列空");
            return;
        }
        for (int i = front; i < front + size(); i++) {
            System.out.println("arr[" + i % maxSize + "]:" + arr[i % maxSize]);
        }
    }

    // 显示队头
    public int peekQueue() {
        if (isEmpty()) {
            throw new RuntimeException("队列空");
        }

        return arr[front];
    }

}