三种方式简单实现栈

一、node节点实现

class Node{
    public Node pre;
    public Node next;
    public int val;
    public Node(int val) {
        this.val = val;
    }
}

public class NodeStack {
    private Node head;
    private Node tail;

    public boolean isEmpty() {
        return head == null;
    }

    public void push(int value) {
        Node node = new Node(value);
        if (isEmpty()){
            head = node;
            tail = node;
            return;
        }
        tail.next = node;
        node.pre = tail;
        tail = node;
    }

    public Integer pop() {
        if (isEmpty()) return null;
        if (tail.pre == null){
            int result = tail.val;
            head = null;
            tail = null;
            return result;
        }
        Node  node = tail;

        tail.pre.next = null;
        node.pre = null;
        return node.val;
    }
    public Integer peek() {
        if (isEmpty()) return null;
        return tail.val;
    }

    public void list() {
        Node current = head;
        while (current.next != null){
            System.out.printf(current.val + " ");
            current = current.next;
        }
        System.out.println(current.val);
    }

}

二、链表实现

public class ListStack {
    private List<Integer> list;
    private int maxSize;

    public ListStack(int maxSize) {
        this.list = new LinkedList<>();
        this.maxSize = maxSize;
    }

    public boolean isFull() {
        return list.size() == maxSize;
    }

    public boolean isEmpty() {
        return list.size() == 0;
    }


    public void push(int value) {
        if (isFull()) return;
        list.add(value);
    }
    public Integer pop() {
        if (isEmpty()) return null;
        Integer result = list.get(list.size() - 1);
        list.remove(list.size() - 1);
        return result;
    }

    public void list() {
        System.out.println(list);
    }

}

三、数组实现

public class XinStack {
    int top = -1;
    int[] intlist;
    int maxSize;

    public XinStack(int maxSize) {
        this.maxSize = maxSize;
        intlist = new int[maxSize];
    }

    public boolean isFull(){
        return top == maxSize - 1;
    }
    public void push(int value){
        if (!isFull()){
            top++;
            intlist[top] = value;
        }else {
            System.out.println("stack is full");
        }
    }

    public int pop(){
        if (top > -1){
            int value = intlist[top];
            top--;
            return value;
        }else {
            throw new RuntimeException("元素已经没有了");
        }
    }
    public void list(){
        if (maxSize < 0){
            return;
        }
        for (int i = top; i >= 0 ; i--) {
            System.out.printf(intlist[i] + " ");
        }
        System.out.print("\n");
    }
}