理论补充

先进后出 FILO（First-Input-Last-Out）的有序列表，限制线性表中元素的插入和删除只能在线性表的同一端进行

• 栈顶：变化的一端
• 栈底:固定的一端

代码实现

2.1 数组模拟栈

package com.b0.stack;

import java.util.Scanner;

public class ArrayStackDemo {
    public static void main(String[] args) {
        ArrayStack stack = new ArrayStack(5);
        String key = "";
        boolean loop = true;//控制是否退出菜单
        Scanner scanner = new Scanner(System.in);
        while (loop){
            System.out.println("show：表示显示栈");
            System.out.println("exit：退出程序");
            System.out.println("push：入栈");
            System.out.println("pop：出栈");
            System.out.println("请输入你的选择");
            key = scanner.next();
            switch (key){
                case "show":
                    stack.list();
                    break;
                case "push":
                    System.out.println("请输入一个数");
                    int value = scanner.nextInt();
                    stack.push(value);
                    break;
                case "pop":
                    try {
                        int res = stack.pop();
                        System.out.println("出栈数据是："+res);
                    }catch (Exception e){
                        System.out.println(e.getMessage());
                    }
                    break;
                case "exit":
                    scanner.close();
                    loop = false;
                    break;
                default:
                    break;
            }
        }
        System.out.println("程序退出~");
    }
}
class ArrayStack{
    private int maxSize;//栈的大小
    private int[] stack;//数组模拟栈
    private int top = -1;//栈顶，初始化为-1
    //构造器
    public ArrayStack(int maxSize) {
        this.maxSize = maxSize;
        stack = new int[this.maxSize];
    }
    //判断栈满
    public boolean isFull(){
        return top == maxSize-1;
    }
    //栈空
    public boolean isEmpty(){
        return top == -1;
    }
    //入栈
    public void push(int num){
        //判断是否栈满
        if (isFull()){
            System.out.println("栈满");
            return;
        }
        top++;
        stack[top] = num;
    }
    //出栈
    public int pop(){
        //判断是否栈空
        if (isEmpty()){
            //抛出异常
            throw new RuntimeException("栈空，没有数据！");
        }
        int value = stack[top];
        top--;
        return value;
    }
    //遍历栈
    public void list(){
        if (isEmpty()){
            System.out.println("栈空！");
            return;
        }
        while (top != -1){
            //从栈顶开始遍历
            System.out.println(stack[top]);
            top--;
        }
    }
}

2.2 链表模拟栈（头插法）

package com.b0.stack;

public class LinkedStackDemo {
    public static void main(String[] args) {
        LinkedStack linkedStack = new LinkedStack();
        linkedStack.push(1);
        linkedStack.push(2);
        linkedStack.push(3);
        linkedStack.push(4);
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
    }
}
class LinkedStack{
    //头节点
    Node head = new Node(0);
    //栈空,尾插法
    public boolean isEmpty(){
        return head.next == null;
    }
    //入栈，头插法
    public void push(int num){
        Node node = new Node(num);
        if (isEmpty()){
            head.next = node;
        }
        node.next = head.next;
        head.next = node;
    }
    public int pop(){
        if (isEmpty()){
            //抛出异常
            throw new RuntimeException("栈空，没有数据！");
        }
        //定义零时变量，不修改head指针指向
        Node cur = head;
        int value = cur.next.no;
        cur.next = cur.next.next;
        return value;
    }
}
class Node{
    public int no;
    public Node next;

    public Node(int no) {
        this.no = no;
    }
}

2.3 链表模拟栈（尾插法，不推荐）

package com.b0.stack;

public class LinkedStackDemo {
    public static void main(String[] args) {
        LinkedStack linkedStack = new LinkedStack();
        linkedStack.push(1);
        linkedStack.push(2);
        linkedStack.push(3);
        linkedStack.push(4);
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
        System.out.println("出栈值为："+linkedStack.pop());
    }
}
class LinkedStack{
    //头节点
    Node head = new Node(0);
    //栈空
    public boolean isEmpty(){
        return head.next == null;
    }
    //入栈
    public void push(int num){
        Node node = new Node(num);
        Node cur = head;
        while (true){
            if (cur.next == null)break;
            cur = cur.next;
        }
        cur.next = node;
    }
    //出栈
    public int pop(){
        if (isEmpty()){
            //抛出异常
            throw new RuntimeException("栈空，没有数据！");
        }
        //定义零时变量，不修改head指针指向
        Node cur = head;
        int value;
        while (true){
            if (cur.next.next == null){
                value = cur.next.no;
                cur.next = null;
                break;
            }
           cur = cur.next;
        }
        return value;
    }
}
class Node{
    public int no;
    public Node next;

    public Node(int no) {
        this.no = no;
    }
}