4.数据结构--链表

public class LinkedList<E> {
    private class Node{
        public E e;
        public Node next;

        public Node(E e,Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e){
            this(e,null);
        }

        public Node(){
            this(null,null);
        }

        @Override
        public String toString(){
            return e.toString();
        }
    }

    private Node head;
    int size;

    public LinkedList(){
        head = null;
        size =0;
    }

    //获取链表中的元素个数
    public int getSize(){
        return size;
    }

    //返回链表是否为空
    public boolean isEmpty(){
        return size == 0;
    }

    //在链表头添加新的元素e
    public void addFirst(E e){
//        Node node = new Node(e);
//        node.next = head;
//        head = node;

        head = new Node(e,head);
        size ++;
    }

    //在链表的index位置添加新元素e
    public void add(int index,E e){
        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Illegal index.");

        if(index == 0)
            addFirst(e);
        else{
            Node prev = head;
            for(int i = 0;i < index -1;i ++)
                prev =prev.next;
//            Node node =new Node(e);
//            node.next = prev.next;
//            prev.next = node;

            prev.next =new Node(e,prev.next);
            size ++;
        }
    }

    //在链表末尾添加新的元素e
    public void addLast(E e){
        add(size,e);
    }
}

public class LinkedList<E> {
    private class Node{
        public E e;
        public Node next;

        public Node(E e,Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e){
            this(e,null);
        }

        public Node(){
            this(null,null);
        }

        @Override
        public String toString(){
            return e.toString();
        }
    }

    private Node dummyHead;
    private int size;

    public LinkedList(){
        dummyHead = new Node(null,null);
        size =0;
    }

    //获取链表中的元素个数
    public int getSize(){
        return size;
    }

    //返回链表是否为空
    public boolean isEmpty(){
        return size == 0;
    }

    //在链表的index位置添加新元素e
    public void add(int index,E e){
        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Illegal index.");

        Node prev = dummyHead;
        for(int i = 0;i < index;i ++)
            prev =prev.next;

        prev.next =new Node(e,prev.next);
        size ++;
    }

    //在链表头添加新的元素e
    public void addFirst(E e){
        add(0,e);
    }

    //在链表末尾添加新的元素e
    public void addLast(E e){
        add(size,e);
    }
}