双向链表

双向链表跟单链表类似，每个节点多了previous指针，指向前一个元素；还多了一个tail指针指向链表的尾节点；可以从头尾两个方向遍历链表。

代码实现

public class DoubleLinkedList {

    private DoubleNode head;
    private DoubleNode tail;
    private Integer size = 0;

    /**
     * 添加至链表头
     * @param node
     */
    public void addFirst(DoubleNode node) {
        if (head == null) {
            head = node;
            tail = node;
        } else {
                node.next = head;
                head.prev = node;
                head = node;
        }
        size++;
    }

    /**
     * 添加至链表尾
     * @param node
     */
    public void addLast(DoubleNode node) {
        if (tail == null) {
            head = node;
            tail = node;
        } else {
            tail.next = node;
            node.prev = tail;
            tail = node;
        }
        size++;
    }

    /**
     * 按照某属性的顺序添加
     * @param node
     */
    public void addByOrder(DoubleNode node) {
        // 第一个节点
        if (head == null) {
            head = node;
            tail = node;
            size ++;
            return;
        }

        // 新节点比头节点小
        if (node.no <= head.no) {
            node.next = head;
            head.prev = node;
            head = node;
            return;
        }
        //新节点比尾节点大
        if (node.no >= tail.no) {
            node.prev = tail;
            tail.next = node;
            tail = node;
            return;
        }

        // 找到比新节点大的节点
        DoubleNode tmpNode = head;
        while (tmpNode != null && tmpNode.no < node.no) {
            tmpNode = tmpNode.next;
        }
        node.prev = tmpNode.prev.next;
        tmpNode.prev.next = node;
        tmpNode.prev = node;
        node.next = tmpNode;
        size++;
    }

    /**
     * 修改
     * @param node
     */
    public void modify(DoubleNode node) {
        DoubleNode tmp = head;
        while(tmp !=null) {
            if (tmp.no.equals(node.no)) {
                tmp.name = node.name;
                break;
            }
            tmp = tmp.next;
        }
    }

    /**
     * 根据编号获取节点
     * @param no
     * @return
     */
    public DoubleNode query(int no) {
        DoubleNode tmp = head;
        while (tmp != null) {
            if (tmp.no.equals(no)) {
                return tmp;
            }
            tmp = tmp.next;
        }
        return null;
    }

    /**
     * 根据编号删除节点
     * @param no
     */
    public void remove(int no) {
        if (head == null) {
            return;
        }

        if (head == tail) {
            head = null;
            tail = null;
            return;
        }

        //头节点
        if (no == head.no) {
            head.prev = null;
            head = head.next;
            size--;
            return;
        }
        // 尾节点
        if (no == tail.no) {
            tail.prev.next = null;
            tail = tail.prev;
            size--;
            return;
        }

        // 非根节点
        DoubleNode tmp = head.next;
        while (tmp != null) {
            if (no == tmp.no) {
                break;
            }
            tmp = tmp.next;
        }
        // 节点不存在
        if (tmp == null) {
            return;
        }
        tmp.prev.next = tmp.next;
        tmp.next.prev = tmp.prev;
        size--;
    }

    /**
     * 打印
     */
    public void display() {
        if (head == null) {
            System.out.println("This DoubleLinkedList is null.");
            return;
        }
        DoubleNode tmp = head;
        while(tmp != null) {
            System.out.println(tmp.toString());
            tmp = tmp.next;
        }
    }

    /**
     * 获取链表长度
     * @return
     */
    public Integer getSize() {
        return size;
    }
}

 

节点

public class DoubleNode {

    protected Integer no;
    protected String name;
    protected DoubleNode next;
    protected DoubleNode prev;

    public DoubleNode(Integer no, String name) {
        this.no = no;
        this.name = name;
    }

    @Override
    public String toString() {
        return "DoubleNode[" +
                "no=" + no +
                ", name='" + name + '\'' +
                ']';
    }
}