Java实现单链表

真正的动态数据结构（引用和指针）

优点:真正的动态，不需要处理固定容量的问题。

缺点:丧失随机访问的能力。

链表就像寻宝，我们拿到藏宝图开始出发寻宝，每找到一个地方后，里面藏着下一步应该去哪里寻找。一步一步往下找，就能找到宝藏。每个节点都存有数据和下个节点的位置。

将数据存储在节点中,next指向当前节点的下一个节点。

class Node
{
   E e;
   Node next;
}

要想访问这个链表的所有节点，我们必须知道链表的头节点，所以我们定义head，在定义个size记录链表中有几个元素

向链表的头添加元素很简单，我们添加一个node，在把这个nodet指针指下一个节点，这时的head节点就变成我们添加的节点，我们就变成头节点。

所以LinkList类

package com.dsideal.test;

public class LinkList<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;

    private int size;

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

    public int getSize()
    {
        return size;
    }

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

    public void addFirst(E e)
    {
//        Node node = new Node(e);
//        node.next = head;
//        head = node;

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

在链表中间添加元素，我们必须知道在插入节点之前的一个节点是什么。将前一个节点的指针指向我们插入的节点，把我们的插入节点的指针指向下一个节点。

package com.dsideal.test; 
public class LinkList<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;

    private int size;

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

    public int getSize()
    {
        return size;
    }

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

    public void addFirst(E e)
    {
//        Node node = new Node(e);
//        node.next = head;
//        head = node;

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

    public void add(int index,E e)
    {
        if (index < 0 || index > size)
        {
            throw new IllegalArgumentException("add is fail,index < 0 or index >= size");
        }
        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 ++;
        }

    }

    public void addLast(E e)
    {
        add(size,e);
    }

    @Override
    public String toString()
    {
        StringBuilder res = new StringBuilder();
        res.append("Link head:");
        Node cur = head;
        while (cur != null)
        {
            res.append(cur + "->");
            cur = cur.next;
        }
        res.append("NULL");
        return res.toString();
    }
}

这时我们发现，当add插入index等于零的时候，要做个判断。所以我们引入一个虚拟的头节点。Node dunmmy = new Node(null,null);删除节点，找到要删除节点的上一个节点，将

他的指针指向删除节点的下一个节点，将我们删除节点的next指向null。

所以LinkLIst类变为

public class LinkList<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 LinkList()
    {
        dummyHead = new Node(null, null);
        size = 0;
    }

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

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

    //增加链表头元素
    public void addFirst(E e)
    {
//        Node node = new Node(e);
//        node.next = head;
//        head = node;
        add(0, e);
    }

    //增加链表元素个数
    public void add(int index, E e)
    {
        if (index < 0 || index > size)
        {
            throw new IllegalArgumentException("index < 0 or index > size,add is fail.");
        }

        Node prev = dummyHead;
        for (int i = 0; i < index; i++)
        {
            prev = prev.next;
        }
//            Node node = new Node(e);
//            node.next = prev.next;
//            prev.next = node;
        prev.next = new Node(e, prev.next);
        size++;
    }

    //添加链表末尾元素
    public void addLast(E e)
    {
        add(size, e);
    }

    //获取元素index
    public E get(int index)
    {
        if (index < 0 || index >= size)
        {
            throw new IllegalArgumentException("get is fail,index < 0 or index > size");
        }
        Node cur = dummyHead.next;
        for (int i = 0;i < index;++i)
        {
            cur = cur.next;
        }
        return cur.e;
    }

    //获取第一个元素
    public E getFirst()
    {
        return get(0);
    }

    //获取最后一个元素
    public E getLast()
    {
        return get(size - 1);
    }

    //判读是否包含
    public boolean contains(E e)
    {
        Node cur = dummyHead.next;
        while (cur != null)
        {
            if (cur.e.equals(e))
            {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //修改值
    public void set(int index,E e)
    {
        if (index < 0 || index >= size)
        {
            throw new IllegalArgumentException("set is fail,index < 0 or index > size");
        }
        Node cur = dummyHead.next;
        for (int i = 0;i < index;++i)
        {
            cur = cur.next;
        }
        cur.e = e;
    }

    //删除元素
    public E remove(int index)
    {
        if (index < 0 || index >= size)
        {

        }
        Node prev = dummyHead;
        for (int i = 0;i < index;++i)
        {
            prev = prev.next;
        }
        //删除的元素
        Node retNode = prev.next;
        prev.next = retNode.next;
        retNode.next = null;//删除元素的指向下一个地址为空
        size-- ;
        return retNode.e;
    }
    //删除第一元素
    public E removeFirst()
    {
        return remove(0);
    }
    //删除最后一个元素
    public E removeLast()
    {
        return remove(size - 1);
    }
    @Override
    public String toString()
    {
        StringBuilder res = new StringBuilder("");
        for (Node cur = dummyHead.next; cur != null; cur = cur.next)
        {
            res.append(cur + "->");
        }
        res.append("NULL");
        return res.toString();
    }
}

用链表实现栈

public class LinkListStack<E> implements Stack<E>
{
    private LinkList<E> linkList;

    public LinkListStack()
    {
        linkList = new LinkList<>();
    }

    @Override
    public int getSize()
    {
        return linkList.getSize();
    }

    @Override
    public boolean isEmpty()
    {
        return linkList.isEmpty();
    }

    @Override
    public void push(E e)
    {
        linkList.addFirst(e);
    }

    @Override
    public E pop()
    {
        return linkList.removeFirst();
    }

    @Override
    public E peek()
    {
        return linkList.getFirst();
    }

    @Override
    public String toString()
    {
        StringBuilder res = new StringBuilder();
        res.append("Stack top[");
        res.append(linkList);
        res.append("] tail");
        return res.toString();
    }
}

链表实现队列，优化算法变为O(1)级别的

public class LinkListQueue<E> implements Queue<E>
{
    //内置节点
    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,tail;

    private int size;

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

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

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    @Override
    public void enqueue(E e)  {
        if (tail == null)
        {
            tail = new Node(e);
            head = tail;
        }else {
            tail.next = new Node(e);
            tail = tail.next;
            tail.next = null;
        }
        size ++;
    }

    @Override
    public E dequeue()  {
        if (isEmpty())
        {
            throw new IllegalArgumentException("dequeue is fail,queue is isEmpty");
        }
        Node retNode = head;
        head = retNode.next;
        retNode.next = null;
        if (head == null)
        {
            tail = null;
        }
        size--;
        return retNode.e;
    }

    @Override
    public E getFront() {
        if (isEmpty())
        {
            throw new IllegalArgumentException("Queue is isEmpty,so getFront is fail.");
        }
        return head.e;
    }
    @Override
    public String toString()
    {
        StringBuffer str = new StringBuffer("");
        str.append("LinkListQueue: head:");
        Node cur = head;
        while (cur != null)
        {
            str.append(cur + "->");
            cur = cur.next;
        }
        str.append("NULL");
        return str.toString();
    }
}