public static void main(String[] args) {
        Stack<Integer> stack=new Stack<>();
        //入棧
        stack.push(1);
        stack.push(2);
        stack.push(3);
        //獲取有效個(gè)數(shù)大小
        System.out.println(stack.size());//3
        //獲取棧頂元素
        System.out.println(stack.peek());//3
        //出棧
        stack.pop();
        //獲取棧頂元素
        System.out.println(stack.peek());//2
        //查找元素下標(biāo)
        System.out.println(stack.search(2));
    }

//數(shù)組模擬實(shí)現(xiàn)棧
public class MyStack {
    //元素
    public int[] n;
    //有效元素大小
    public int usedsize;
    //構(gòu)造方法
    public MyStack(int[] n) {
        this.n = n;
    }
    //入棧:將元素進(jìn)行插入
    //1.判斷是否滿了，滿了用Arrays.copyOf進(jìn)行擴(kuò)容
    //1.用元素放入數(shù)組中，
    //2.元素個(gè)數(shù)增加
    public void push(int x){
        if(isFull()){
          this.n= Arrays.copyOf(n,2*n.length);
        }  
        n[usedsize]=x;
         usedsize++;
    }
    private boolean isFull(){
        return usedsize==n.length;
    }
    //出棧：將棧頂元素拿出
    //1.判斷棧是否為空；
    // 2.將棧中元素減減即可
    public int pop(){
        if(empty()){
            return -1;
        }
        int val=n[usedsize-1];
         usedsize--;
         return val;
    }
    //獲取棧頂元素
    //1.判斷棧是否為空,如果為空拋出異常
    // 2.獲取棧中元素
    public int peek(){
        if(empty()){
             throw new EmptyStackException();
        }
        return n[usedsize-1];
    }
    //判斷棧是否為空
    //看其有效個(gè)數(shù)是否為0
    public boolean empty()throws EmptyStackException{
          return this.usedsize==0;
    }
}

 public static void main(String[] args) {
        Queue<Integer> queue=new LinkedList<>();
        Queue<Integer> queue1=new ArrayDeque<>();
        Queue<Integer> queue2=new PriorityQueue<>();
    }

    public static void main(String[] args) {
        Queue<Integer> queue=new LinkedList<>();
        //入隊(duì)
        queue.offer(1);
        queue.offer(2);
        queue.offer(3);
        //獲取有效元素個(gè)數(shù)
        System.out.println(queue.size());//3
        //獲取隊(duì)頭元素
        System.out.println(queue.peek());//1
        //出隊(duì)
        System.out.println(queue.poll());//1
    }

public class MyQueue {
     //創(chuàng)建節(jié)點(diǎn)類
    static class ListNode{
        public int val;
        public ListNode prev;
        public ListNode next;
         public ListNode(int val) {
             this.val = val;
         }
     }
     public ListNode first=null;
     public ListNode last=null;
     public int usedSize=0;
     //入隊(duì)
    //判斷是否為空,如果為空將頭尾節(jié)點(diǎn)都等于該新節(jié)點(diǎn)
    //如果不是，將節(jié)點(diǎn)添加到隊(duì)尾
    //有效元素個(gè)數(shù)增加
    public void offer(int val){
        ListNode listNode=new ListNode(val);
        if(isEmpty()){
            first=last=listNode;
        }else{
            last.next=listNode;
            listNode.prev=last;
            last=listNode;
        }
        usedSize++;
    }
    //出隊(duì)
    //判斷隊(duì)列是否為空；
    //出隊(duì)頭元素,將隊(duì)頭指針向后移動(dòng)
    //使用元素個(gè)數(shù)減少
    public int poll(){
        if(isEmpty()){
            return -1;
        }
        int val= first.val;
        first=first.next;
        if(first!=null){
            first.prev=null;
        }
        return val;
    }
    //獲取隊(duì)頭元素
    //判斷隊(duì)列是否為空
    //如果不為空，直接返回隊(duì)頭元素
    public int peek(){
        if(isEmpty()){
            return -1;
        }
        return first.val;
    }
    //判斷是否為空
    //判斷有效元素個(gè)數(shù)是否為0
    public boolean isEmpty(){
        return usedSize==0;
    }
}