双向链表的JAVA实现

双向链表

双向链表(双链表)是链表的一种。和单链表一样，双链表也是由节点组成，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。一般我们都构造双向循环链表。

双向链表示意图：

java双链表代码实现：

package com.ski.codebox.ds;

/**
 * Created by ski.zhou on 26/03/2018.
 * 用java实现一个双向链表
 */
public class DoubleLink<T> {

    //表头
    private DNode mHead;
    //节点个数
    private int mCount;

    //节点对应结构体
    private class DNode<T> {

        public DNode prev;
        public DNode next;
        public T value;

        public DNode(DNode prev, DNode next, T value) {
            this.prev = prev;
            this.next = next;
            this.value = value;
        }
    }

    //构造函数
    public DoubleLink() {
        //创建表头
        mHead = new DNode(null, null, null);
        mHead.prev = mHead.next = mHead;
        //初始化节点个数
        mCount = 0;
    }

    //返回节点数目
    public int size() {
        return mCount;
    }

    //判断列表是否为空
    public boolean isEmpty() {
        return mCount == 0;
    }

    public T get(int index) {
        return getNode(index).value;
    }

    //获取链表index处的节点
    private DNode getNode(int index) {
        if (index < 0 || index >= mCount)
            throw new IndexOutOfBoundsException();
        //正向查找
        if (index <= mCount / 2) {
            DNode node = mHead.next;
            for (int i = 0; i < index; i++) {
                node = node.next;
            }
            return node;
        }
        //反向查找
        DNode node = mHead.prev;
        int rIndex = mCount - index - 1;
        for (int j = 0; j < rIndex; j++) {
            node = node.prev;
        }
        return node;
    }

    //获取第一个节点
    public T getFirst() {
        return getNode(0).value;
    }

    //获取最后一个节点
    public T getLast() {
        return getNode(mCount - 1).value;
    }

    //将节点插入index位置前
    public void insert(int index, T t) {

        if (index == 0) {
            DNode node = new DNode(mHead, mHead.next, t);
            mHead.next.prev = node;
            mHead.next = node;
            mCount++;
            return;
        }
        DNode iNode = getNode(index);
        DNode tNode = new DNode(iNode.prev, iNode, t);
        iNode.prev.next = tNode;
        iNode.prev = tNode;
        mCount++;
        return;
    }

    //插入第一个节点处
    public void insertFirst(T t) {
        this.insert(0, t);
    }

    //追加到链表末尾
    public void appendLast(T t) {
        DNode node = new DNode(mHead, mHead.next, t);
        mHead.prev.next = node;
        mHead.next = node;
        mCount++;
        return;
    }

    //删除index处的节点
    public void del(int index) {
        DNode inode = getNode(index);
        inode.prev.next = inode.prev;
        inode.next.prev = inode.next;
        inode = null;
        mCount--;
    }

    //删除第一个节点
    public void delFirst() {
        del(0);
    }

    //删除最后一个节点
    public void delLast() {
        del(mCount - 1);
    }
}

/**
 * 双向链表测试
 */
class DoubleLinkTest {

    //int
    private static void intTest() {
        int[] iarr = {10, 20, 30, 40};
        System.out.println("\n----int_test----");
        DoubleLink doubleLink = new DoubleLink();
        doubleLink.insert(0, 20);
        doubleLink.appendLast(10);
        doubleLink.insertFirst(5);

        System.out.printf("isEmpty()=%b\n", doubleLink.isEmpty());
        System.out.printf("size()=%d\n", doubleLink.size());

        for (int i = 0; i < doubleLink.size(); i++) {
            System.out.println("doubleLink(" + i + ")=" + doubleLink.get(i));
        }

    }

    //String
    private static void stringTest() {
        String[] strs = {"one", "two", "three", "four"};
        System.out.println("\n----string_test----");
        DoubleLink doubleLink = new DoubleLink();
        doubleLink.insert(0, strs[1]);
        doubleLink.appendLast(strs[3]);
        doubleLink.insertFirst(strs[2]);

        System.out.printf("isEmpty()=%b\n", doubleLink.isEmpty());
        System.out.printf("size()=%d\n", doubleLink.size());

        for (int i = 0; i < doubleLink.size(); i++) {
            System.out.println("doubleLink(" + i + ")=" + doubleLink.get(i));
        }

    }

    //对象
    private static void objTest() {
        Foo[] foos = new Foo[]{new Foo(1, "tom"),
                new Foo(2, "jerry"),
                new Foo(3, "mary"),
                new Foo(4, "fuck")
        };

        System.out.println("\n----obj_test----");
        DoubleLink doubleLink = new DoubleLink();
        doubleLink.insert(0, foos[2]);
        doubleLink.appendLast(foos[3]);
        doubleLink.insertFirst(foos[2]);

        System.out.printf("isEmpty()=%b\n", doubleLink.isEmpty());
        System.out.printf("size()=%d\n", doubleLink.size());

        for (int i = 0; i < doubleLink.size(); i++) {
            System.out.println("doubleLink(" + i + ")=" + doubleLink.get(i).toString());
        }

    }

    //内部类
    private static class Foo {
        private int id;
        private String name;

        public Foo(int id, String name) {
            this.id = id;
            this.name = name;
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "Foo{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

    public static void main(String[] args) {
        intTest();
        stringTest();
        objTest();
    }
}