动态（单）链表代码实现

为了表示每个数据元素ai与其直接后继续元素ai+1之间的逻辑关系，对数据元素ai来说，处理存储本身的信息之外，还需要存储一个指示其直接后继的信息。我们把存储数据元素信息的域称为数据域，把存储直接后继位置的域称为指针域。

n个结点链结成一个链表，即为线性表的链式存储结构，因为次链表的每个结点中只包含一个指针域，所以叫做单链表。

头结点与头指针

头结点是指链表中的第一个结点，有真实头结点和虚拟头结点之分

真实头结点：其第一个结点用于存储数据

虚拟头结点：其第一个结点不许存储数据

头指针：仅仅是一个引用变量，存储头结点地址的指针而已

底层与线性表相似 可继承其接口：https://blog.youkuaiyun.com/m0_49201977/article/details/120607659?spm=1001.2014.3001.5501

public class LinkedSinglyList<E> implements List<E> {

    //定义结点对象
    private class Node{
        E data; //数据域
        Node next; //指针域

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

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

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

    private Node head; //头指针
    private Node tail; //尾指针
    private int size; //元素个数

    public LinkedSinglyList(){
        head = null;
        tail = null;
        size = 0;
    }

    public LinkedSinglyList(E[] arr){
        if (arr == null || arr.length == 0){
            throw new IllegalArgumentException("arr is null");
        }
        for (int i =0; i < arr.length; i++){
            add(arr[i]);
        }
    }
    @Override
    public void add(E element) {
        add(size, element);
    }

    @Override
    public void add(int index, E element) {
        if (index < 0 || index > size){
            throw new IllegalArgumentException("add index out of range");
        }
        //创建元素结点
        Node n = new Node(element);

        if (size == 0){
            head = n;
            tail = n;
        }else if (index == 0){
            n.next = head;
            head = n;
        }else if (index == size){
            tail.next = n;
            tail = n;
        }else {
            Node p = head;
            for (int i = 0; i < index - 1; i++) {
                p = p.next;
            }
            n.next = p.next;
            p.next = n;
        }
        size++;
    }

    @Override
    public void remove(E element) {
        int index = indexOf(element);
        if (index != -1){
            remove(index);
        }
    }

    @Override
    public E remove(int index) {
        if (index < 0 || index >= size){
            throw new IllegalArgumentException();
        }
        E ret = null;
        if (size == 1){
            ret = head.data;
            head = null;
            tail = null;
        }else if (index == 0){
            Node n = head;
            ret = n.data;
            head = n.next;
            n.next = null;
        }else if (index == size - 1){
            Node p = head;
            while (p.next != tail){
                p = p.next;
            }
            ret = tail.data;
            p.next = null;
            tail = p;
        }else {
            Node p = head;
            for (int i = 0; i < index - 1; i++) {
                p = p.next;
            }
            Node n = p.next;
            ret = n.data;
            p.next = n.next;
            n.next = null;
        }
        size--;
        return ret;
    }

    @Override
    public E get(int index) {
        if (index < 0 || index >= size){
            throw new IllegalArgumentException("get index out of range");
        }
        if (index == 0){
            return head.data;
        }else if (index == size - 1){
            return tail.data;
        }else {
            Node p = head;
            for (int i = 0; i < index; i++) {
                p = p.next;
            }
            return p.data;
        }
    }

    @Override
    public E set(int index, E element) {
        if (index < 0 || index >= size){
            throw new IllegalArgumentException("get index out of range");
        }
        E ret = null;
        if (index == 0){
            ret = head.data;
            head.data = element;
        }else if (index == size - 1){
            ret = tail.data;
            tail.data = element;
        }else {
            Node p = head;
            for (int i = 0; i < index; i++) {
                p = p.next;
            }
            ret = p.data;
            p.data = element;
        }
        return ret;
    }

    @Override
    public int size() {
        return size;
    }

    @Override
    public int indexOf(E element) {
        Node p = head;
        int index = 0;
        while (!p.data.equals(element)){
            p = p.next;
            index++;
            if (p == null){
                return -1;
            }
        }
        return index;
    }

    @Override
    public boolean contains(E element) {
        return indexOf(element) != -1;
    }

    @Override
    public boolean isEmpty() {
        return size == 0 && head == null && tail == null;
    }

    @Override
    public void clear() {
        head = null;
        tail = null;
        size = 0;
    }

    @Override
    public void sort(Comparator<E> c) {
        if (c == null){
            throw new IllegalArgumentException("comparator can not be null");
        }
        //此处不能用插入排序
//        for (int i = 0; i < size; i++) {
//            E e = get(i);
//            int j = 0;
//            for (j = i; j > 0 && c.compare(get(j - 1), e) > 0; j--){
//                set(j, get(j - 1));
//            }
//            set(j, e);
//        }
        if (size == 0 || size == 1){
            return;
        }
        Node nodeA = head;
        Node nodeB = nodeA.next;
        while(true){
            while (true){
                if (c.compare(nodeA.data,nodeB.data) > 0){
                    swap(nodeA, nodeB);
                }
                if (nodeB == tail){
                    break;
                }
                nodeB = nodeB.next;
            }
            if (nodeA.next == tail){
                break;
            }
            nodeA = nodeA.next;
            nodeB = nodeA.next;
        }
    }

    private void swap(Node nodeA, Node nodeB) {
        E temp = nodeA.data;
        nodeA.data = nodeB.data;
        nodeB.data = temp;
    }

    @Override
    public List<E> subList(int fromIndex, int toIndex) {
        // 0 <= fromIndex <= toIndex <= size -1 [fromIndex,toIndex]
        if (fromIndex < 0 || toIndex >= size || fromIndex > toIndex){
            throw new IllegalArgumentException("0 <= fromIndex <= toIndex <= size -1");
        }
        LinkedSinglyList<E> list = new LinkedSinglyList<>();
        for (int i = fromIndex; i <=  toIndex ; i++) {
            list.add(get(i));
        }
        Node nodeA = head;
        for (int i = 0; i < fromIndex; i++) {
            nodeA = nodeA.next;
        }
        Node nodeB = head;
        for (int i = 0; i < fromIndex; i++) {
            nodeB = nodeB.next;
        }

        Node p = nodeA;
        while(true){
            list.add(p.data);
            if (p == nodeB){
                break;
            }
            p = p.next;
        }
        return list;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append('[');
        if (isEmpty()){
            sb.append(']');
        }else {
            Node p = head;
            while (true) {
                sb.append(p.data);
                if (p == tail) {
                    sb.append(']');
                    break;
                }
                sb.append(',');
                sb.append(' ');
                p = p.next;
            }
        }
        return sb.toString();
    }

    @Override
    public Iterator<E> iterator() {
        return new LinedSinglyListIterator();
    }
    class LinedSinglyListIterator implements Iterator<E>{
        private Node cur = head;


        @Override
        public boolean hasNext() {
            return cur != null;
        }

        @Override
        public E next() {
            E ret = cur.data;
            cur = cur.next;
            return ret;
        }
    }
}