【数据结构】队列

队列（Queue）是只允许在一端进行插入操作，而在另一端进行删除操作的线性表。

特点

先进先出（First In First Out）的线性表。

Java实现

/** 
 * The Apache License 2.0
 * Copyright (c) 2018 sep6th
 */

public class Queue {

    private long[] arr;
    //有效数据个数
    private int elements;
    //队头
    private int front;
    //队尾
    private int end;

    public Queue() {
        arr = new long[10];
        elements = 0;
        front = 0;
        end = -1;
    }

    public Queue(int maxSize) {
        arr = new long[maxSize];
        elements = 0;
        front = 0;
        end = -1;
    }

    /**
     * 从队尾添加数据
     */
    public void insert(long value) {
        arr[++end] = value;
        elements++;
    }

    /**
     * 删除数据，从队头删除
     */
    public long remove() {
        elements--;
        return arr[front++];
    }

    /**
     * 查看数据，从队头查看
     */
    public long peek() {
        return arr[front];
    }

    /**
     * 判断是否为空
     */
    public boolean isEmpty() {
        return elements == 0;
    }

    /**
     * 判断是否满了
     */
    public boolean isFull() {
        return elements == arr.length;
    }


}

测试

/** 
 * The Apache License 2.0
 * Copyright (c) 2018 sep6th
 */

public class TestQueue {

    public static void main(String[] args) {

        Queue q = new Queue(3);
        q.insert(12);
        q.insert(23);
        q.insert(34);

        System.out.println(q.isFull());
        System.out.println(q.isEmpty());
        System.out.println(q.peek());

    }

}

console

true
false
12

循环队列

/** 
 * The Apache License 2.0
 * Copyright (c) 2018 sep6th
 */

public class CycleQueue {

    private long[] arr;
    //有效数据的大小
    private int elements;
    //队头
    private int front;
    //队尾
    private int end;

    /**
     * 默认构造方法
     */
    public CycleQueue() {
        arr = new long[10];
        elements = 0;
        front = 0;
        end = -1;
    }

    /**
     * 带参数的构造方法，参数为数组的大小
     */
    public CycleQueue(int maxsize) {
        arr = new long[maxsize];
        elements = 0;
        front = 0;
        end = -1;
    }

    /**
     * 添加数据,从队尾插入
     */
    public void insert(long value) {
        if(end == arr.length - 1) {
            end = -1;
        }
        arr[++end] = value;
        elements++;
    }

    /**
     * 删除数据，从队头删除
     */
    public long remove() {
        long value = arr[front++];
        if(front == arr.length) {
            front = 0;
        }
        elements--;
        return value;
    }

    /**
     * 查看数据，从队头查看
     */
    public long peek() {
        return arr[front];
    }

    /**
     * 判断是否为空
     */
    public boolean isEmpty() {
        return elements == 0;
    }

    /**
     * 判断是否满了
     */
    public boolean isFull() {
        return elements == arr.length;
    }

}