第1关：实现基于数组的栈

/**
 * @Author: Vastsea(lyx8851@qq.com)
 * @Date: 2024-03-22 17:56:34
 * @LastEditors: Vastsea(lyx8851@qq.com)
 * @LastEditTime: 2024-03-22 19:06:21
 * @Description: 
 * Link:https://59888888.xyz/
 * Phone:18893558104
 */
package step1;

import java.util.NoSuchElementException;

/**
 * Created by sykus on 2018/1/26.
 */
public class MyStack<T> {
    private T[] S;
    private int top;//栈顶元素下标，初始为-1

    public MyStack() {
        this(1);
    }

    public MyStack(int capacity) {
        S = (T[]) new Object[capacity];
        top = -1;
    }


    /**
     * 入栈操作，把item压入栈中
     *
     * @param item
     */
    public void push(T item) {

        int len = S.length;
        if (top == len - 1) {
            resize(2 * len);
        }
        /********** Begin *********/
        S[++top] = item;
        /********** End *********/
    }


    /**
     * 返回栈顶元素并从栈中移除
     *
     * @return
     */
    public T pop() {
        if (isEmpty()) {
            throw new NoSuchElementException("栈为空！");
        }
        /********** Begin *********/
        return S[top--];
        /********** End *********/
    }

    /**
     * 判断栈是否为空
     *
     * @return
     */
    public boolean isEmpty() {
        if (top < 0)
            return true;
        else
            return false;
    }

    /**
     * 动态扩展数组大小
     *
     * @param capacity
     */
    private void resize(int capacity) {
        assert capacity > top;
        T[] tmp = (T[]) new Object[capacity];
        for (int i = 0; i <= top; i++) {
            tmp[i] = S[i];
        }
        S = tmp;
    }
}

第2关：实现基于链表的栈

/**
 * @Author: Vastsea(lyx8851@qq.com)
 * @Date: 2024-03-22 17:56:34
 * @LastEditors: Vastsea(lyx8851@qq.com)
 * @LastEditTime: 2024-03-22 19:06:21
 * @Description: 
 * Link:https://59888888.xyz/
 * Phone:18893558104
 */

package step2;

import java.util.NoSuchElementException;

/**
 * Created by sykus on 2017/12/29.
 */
public class MyStack<E> {

    private Node<E> head;//头结点
    private Node<E> top;//栈顶
    private int size;//栈中元素个数

    public MyStack() {
        head = new Node<E>();
        head.next = null;
        top = null;//栈顶初始化为null
        size = 0;
    }

    /**
     * 把item压入栈中
     *
     * @param item
     */
    public void push(E item) {
        /********** Begin *********/
        Node tmp = new Node<E>();
        tmp.item = item;
        tmp.next = top;
        top = tmp;
        size++;
        /********** End *********/
    }

    /**
     * 返回它栈顶元素并删除
     */
    public E pop() {
        if (isEmpty())
            throw new NoSuchElementException("栈为空！");

        /********** Begin *********/
        E tmp = top.item;
        top = top.next;
        size--;
        return tmp;
        /********** End *********/
    }

    /**
     * 返回栈中元素个数
     *
     * @return
     */
    public int size() {
        return size;
    }

    /**
     * 判断一个栈是否为空
     *
     * @return
     */
    public boolean isEmpty() {
        return (null == head);
    }

    //链表结点内部类
    private static class Node<E> {
        private E item;
        private Node<E> next;
    }
}

第3关：基于数组的队列

/**
 * @Author: Vastsea(lyx8851@qq.com)
 * @Date: 2024-03-22 17:56:34
 * @LastEditors: Vastsea(lyx8851@qq.com)
 * @LastEditTime: 2024-03-22 19:06:21
 * @Description: 
 * Link:https://59888888.xyz/
 * Phone:18893558104
 */
package step3;

/**
 * Created by zengpeng on 2018/1/30.
 */
public class MyQueue<T> {
    private T[] Q;
    private int head;
    private int tail;
    private int size;

    public MyQueue() {
        this(1);
    }

    public MyQueue(int capacity) {
        Q = (T[]) new Object[capacity];
        size = 0;
        head = tail = 0;
    }

    /**
     * 入队操作
     *
     * @param item
     */
    public void enqueue(T item) {
        /********** Begin *********/
        Q[tail++] = item;
        size++;
        /********** End *********/
    }

    /**
     * 出队操作
     *
     * @return
     */
    public T dequeue() {

        /********** Begin *********/
        size--;
        return Q[head++];
        /********** End *********/
    }

    /**
     * 判断队列是否为空
     * @return
     */
    public boolean isEmpty() {
        return (head == tail) && (size < Q.length);
    }

    public int size() {
        return size;
    }

}

第4关：基于链表的队列

/**
 * @Author: Vastsea(lyx8851@qq.com)
 * @Date: 2024-03-22 17:56:34
 * @LastEditors: Vastsea(lyx8851@qq.com)
 * @LastEditTime: 2024-03-22 19:06:21
 * @Description: 
 * Link:https://59888888.xyz/
 * Phone:18893558104
 */
package step4;

import java.util.NoSuchElementException;

/**
 * Created by sykus on 2017/12/29.
 */
public class MyQueue<T> {

    private Node<T> head;// 头结点，不存数据
    private Node<T> front;//指向队头结点
    private Node<T> tail;//指向队尾结点
    private int size;


    public MyQueue() {
        head = new Node<T>();
        front = tail = null;
        size = 0;
    }

    /**
     * 入队
     *
     * @param item
     */
    public void enqueue(T item) {
        /********** Begin *********/
        Node tmp = new Node<T>();
        tmp.item = item;
        tmp.next = null;
        if (isEmpty()) {
            head.next = front = tail = tmp;
        }else{
            tail.next = tmp;
            tail = tmp;
        }
        size++;
        /********** End *********/

    }

    /**
     * 出队
     *
     * @return
     */
    public T dequeue() {
        if (isEmpty())
            throw new NoSuchElementException("队列为空！");

        /********** Begin *********/
        T tmp = front.item;
        front = front.next;
        head.next = front;
        if (front == null) {
            tail = null;
        }
        size--;
        return tmp;
        /********** End *********/

    }

    /**
     * 返回队列中元素数量
     *
     * @return
     */
    public int size() {
        return size;
    }

    /**
     * 判断一个队列是否为空
     *
     * @return
     */
    public boolean isEmpty() {
        return (front == null);
    }

    /**
     * 链表结点内部类
     */
    private static class Node<E> {
        private E item;
        private Node<E> next;
    }
}

整个活，玩一下哈哈