队列(Queue)

队列特点

• 队列是一个有序列表,可以用数组或者链表实现
• 遵循先进先出的特点,即先进入队列的数据,要先取出.后存入的数据后取出

例如小朋友排队打针,先排队的先打针,后排队的后打针,不准插队,不准谦让!!!

 

/**
 * 环形队列
 * @author Haidnor
 * @creat 2019-12-12-11:35
 */
public class CircleQueue {
    private int front = -1;
    private int rear = -1;
    private int maxSize = 0;
    private Integer[] arr;

    public CircleQueue(int maxSize) {
        this.maxSize = maxSize;
        this.arr = new Integer[maxSize];
    }

    /**
     * Add data to the queue
     * @param num
     */
    public void add(int num){
        if(isEmpty()) {
            front = front + 1;
            arr[front] = num;
            rear ++;
        } else if(isFull()) {
            throw new RuntimeException("The queue is full and data cannot be added");
        } else {
            rear = (rear + 1) % maxSize;
            arr[rear] = num;
        }
    }

    /**
     * Get the header data from the queue
     * @return
     */
    public int get() {
        if(isEmpty()) {
            throw new RuntimeException("The queue is empty and the data cannot be retrieved");
        } else {
            if (front == rear & front + 1 == maxSize) {
                int value = arr[front];
                arr[front] = null;
                front = rear = -1;
                return value;
            } else if (front == rear & front == 0) {
                int value = arr[front];
                arr[front] = null;
                front = rear = -1;
                return value;
            } else {
                int value = arr[front];
                arr[front] = null;
                front = (front + 1) % maxSize;
                return value;
            }
        }
    }

    /**
     * Determines if the queue is empty
     * @return
     */
    public Boolean isEmpty() {
        return front == -1;
    }

    /**
     * Determine if the queue is full
     * @return
     */
    public Boolean isFull() {
        if (front == rear & rear == 0) {
            return false;
        } else if (rear + 1 == maxSize) {
            if (front == 0) {
                return true;
            }
        } else if (rear + 1 == front) {
            return true;
        }
        return false;
    }

    public void show() {
        if (isEmpty()) {
            System.out.println("The queue is empty!");
            return;
        }
        if (rear == front | rear > front) {
            for (int i = front; i < arr.length; i++) {
                System.out.printf("arr[%d]:%d
",i,arr[i]);
            }
        } else {
            for (int i = front; i < arr.length; i++) {
                System.out.printf("arr[%d]:%d
",i,arr[i]);
            }
            for (int i = rear; i < front; i++) {
                System.out.printf("arr[%d]:%d
",i,arr[i]);
            }
        }
    }

}

import java.util.Scanner;

/**
 * @author Haidnor
 * @creat 2020-03-12-16:05
 */
public class CircleQueueTest {
    public static void main(String[] args) {
        CircleQueue queue = new CircleQueue(5);

        Scanner scanner = new Scanner(System.in);
        Boolean loop = true;
        while (loop) {
            System.out.println("
s(show): 查看队列");
            System.out.println("a(add): 加入数据");
            System.out.println("g(get): 取出数据");
            System.out.println("e(exit): 退出程序");
            System.out.print(">>> 请输入指令:");
            char command = scanner.next().charAt(0);
            switch (command) {
                case 's' :
                    queue.show();
                    break;
                case 'a' :
                    System.out.print(">>>输入数字:");
                    try {
                        int num = scanner.nextInt();
                        queue.add(num);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'g' :
                    try {
                        int num = queue.get();
                        System.out.println("取出的数字为:" + num);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'e' :
                    scanner.close();
                    loop = false;
                    break;
                default :
                    break;
            }
        }
        System.out.println("已终止程序!");
    }
}