Java数据结构之链表相关知识总结

一、链表

1.1 概述

链表是真正动态的数据结构，最简单的动态数据结构，基本用于辅助组成其他数据结构。

数据存储在“节点”（Node）中

优点：真正的动态，不需要处理固定容量的问题
缺点：丧失了随机访问的能力

1.2 链表使用的基本功能

定义Node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();
        }
    }

向链表中添加元素

具体代码实现：

 //向链表中间添加元素
    //在链表的index(0-based)位置添加新的元素e
    public void add(int index, E e){
        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Illeagl failed.");
        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++;
    }

向链表中删除元素

具体代码实现：

//链表中删除index(0-based)位置的元素，返回删除的元素
    public E remove(int index){
        if(index < 0 || index >= size)
            throw new IllegalArgumentException("Remove failed.Illeagl failed.");
        Node pre = dummyHead;
        for (int i = 0; i < index; i++) {
            pre = pre.next;
        }
        Node retNode = pre.next;
        pre.next = retNode.next;
        retNode.next = null;
        size--;

        return retNode.e;
    }

链表功能的实现及测试类

public class LinkedList {
    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;
    }

    //向链表头添加元素
    public void addFirst(E e){
//        Node node = new Node(e);
//        node.next = head;
//        head = node;

        add(0, e);
    }

    //向链表中间添加元素
    //在链表的index(0-based)位置添加新的元素e
    public void add(int index, E e){
        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Illeagl failed.");
        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++;
    }

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

    //获得链表的第index(0-based)个位置的元素
    //在链表中不是一个常用的操作
    public E get(int index){
        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Illeagl failed.");
        Node cur = dummyHead.next;
        for (int i = 0; i < index; i++) {
            cur = cur.next;
        }
        return cur.e;
    }

    //获得链表的第一个元素
    public E getFirst(){
        return get(0);
    }

    //获得链表的最后一个元素
    public E getLast(){
        return get(size - 1);
    }

    //修改链表的第index(0-based)个位置的元素
    //在链表中不是一个常用的操作
    public void set(int index, E e){
        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed.Illeagl failed.");
        Node cur = dummyHead.next;
        for (int i = 0; i < index; i++) {
            cur = cur.next;
        }
        cur.e = e;
    }

    //查找链表中是否有元素e
    public boolean contains(E e){
        Node cur = dummyHead.next;
        while(cur != null){
            if(cur.e.equals(e)){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //链表中删除index(0-based)位置的元素，返回删除的元素
    public E remove(int index){
        if(index < 0 || index >= size)
            throw new IllegalArgumentException("Remove failed.Illeagl failed.");
        Node pre = dummyHead;
        for (int i = 0; i < index; i++) {
            pre = pre.next;
        }
        Node retNode = pre.next;
        pre.next = retNode.next;
        retNode.next = null;
        size--;

        return retNode.e;
    }

    //从链表中删除第一个元素
    public E removeFirst(){
        return remove(0);
    }

    //从链表中删除最后一个元素
    public E removeLast(){
        return remove(size - 1);
    }
    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();

//        Node cur = dummyHead.next;
//        while (cur != null){
//            res.append(cur + "->");
//            cur = cur.next;
//        }

        for (Node cur = dummyHead.next; cur != null; cur = cur.next){
            res.append(cur + "->");
        }
        res.append("null");
        return res.toString();
    }
    public static void main(String[] args) {
        LinkedList linkedList = new LinkedList<>();
        for (int i = 0; i < 5; i++) {
            linkedList.addFirst(i);
            System.out.println(linkedList);
        }

        linkedList.add(2, 666);
        System.out.println(linkedList);


        linkedList.remove(2);
        System.out.println(linkedList);

        linkedList.removeFirst();
        System.out.println(linkedList);

        linkedList.removeLast();
        System.out.println(linkedList);
    }
}

二、链表实现栈操作

使用第二章中的栈接口，创建第一节中的链表实现对象，实现栈的操作，具体如下：

public class LinkedListStack implements Stack {
    private LinkedList list;
    public LinkedListStack(){
        list = new LinkedList<>();
    }

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

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

    @Override
    public void push(E value) {
        list.addFirst(value);
    }

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

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

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("Stack : top");
        res.append(list);
        return res.toString();
    }

    public static void main(String[] args) {
        LinkedListStack stack = new LinkedListStack<>();
        for (int i = 0; i < 5; i++) {
            stack.push(i);
            System.out.println(stack);
        }

        stack.pop();
        System.out.println(stack);
    }
}

三、链表实现队列操作

使用第二章中的队列接口，创建无头节点的链表实现队列操作，具体如下：

public class LinkedListQueue implements Queue {
    private class Node{
        public E e;
        public LinkedListQueue.Node next;

        public Node(E e, LinkedListQueue.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 LinkedListQueue(){
        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;
        }
        size++;
    }

    @Override
    public E dequeue() {
        if (isEmpty())
            throw new IllegalArgumentException("Cannot dequeue form any empty queue.");
        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if (head == null)
            tail = null;
        return retNode.e;
    }

    @Override
    public E getFront() {
        if (isEmpty())
            throw new IllegalArgumentException("Cannot getFront form any empty queue.");
        return head.e;
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("Queue : front ");

        Node cur = head;
        while (cur != null){
            res.append(cur + "->");
            cur = cur.next;
        }

        res.append("Null tail");
        return res.toString();
    }

    public static void main(String[] args) {
        LinkedListQueue queue = new LinkedListQueue<>();
        for (int i = 0; i < 10; i++) {
            queue.enqueue(i);
            System.out.println(queue);

            if(i % 3 == 2){
                queue.dequeue();
                System.out.println(queue);
            }
        }

    }
}

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