双向链表

1.双向链表和单向链表的区别在于双向链表可以从两端遍历，每个节点保存自己的前去节点和后继节点。

 2.实现双向链表

package signle;

/**
 * @Author lizhilong
 * @create 2019/11/8 17:51
 * @desc
 */
public class DoubleDirectionLinkedList {

    private int size;

    private Node head;

    private Node tail;

    public DoubleDirectionLinkedList() {
        this.size = 0;
        this.head = null;
        this.tail = null;
    }

    /**
     * 往头元素前添加
     *
     * @param data
     * @return
     */
    public Object addBeforeHead(Object data) {
        Node newNode = new Node(data);
        if (size == 0) {
            newNode.pre = null;
            newNode.next = null;
            head = newNode;
            tail = newNode;
        } else {
            newNode.next = head;
            head.pre = newNode;
            head = newNode;
        }
        size++;
        return data;
    }

    /**
     * 往尾元素后添加
     *
     * @param data
     * @return
     */
    public Object addAfterTail(Object data) {
        Node newNode = new Node(data);
        if (size == 0) {
            newNode.pre = null;
            newNode.next = null;
            head = newNode;
            tail = newNode;
        } else {
            tail.next = newNode;
            newNode.pre = tail;
            tail = newNode;
        }
        size++;
        return data;
    }

    /**
     * 从头元素删除
     *
     * @return
     */
    public Object removeFromHead() {
        Object data = head.data;
        head = head.next;
        size--;
        return data;
    }

    /**
     * 从尾元素删除
     *
     * @return
     */
    public Object removeFromTail() {
        Object data = tail.data;
        tail.pre.next = null;
        size--;
        return data;
    }

    /**
     * 删除指定元素
     *
     * @param object
     * @return
     */
    public boolean remove(Object object) {
        if (size == 0) {
            return false;
        }
        Node node = head;
        while (node.data != object) {
            node = node.next;
        }
        node.next.pre = node.pre;
        node.pre.next = node.next;
        return true;
    }

    /**
     * 查找指定元素
     *
     * @param data
     * @return
     */
    public boolean find(Object data) {
        if (size == 0) {
            return false;
        }
        Node h = head;
        int index = 0;
        while (h.data != data) {
                index++;
                if(index == size){
                    break;
                }
                h = h.next;
        }
        if (index < size) {
            return true;
        }else{
            return false;
        }
    }


    public void displayFromHead() {
        Node current = head;
        StringBuilder builder = new StringBuilder();
        builder.append("头---->尾：[");
        while (current.next != null) {
            builder.append(current.data.toString() + "->");
            current = current.next;
        }
        builder.append(current.data.toString());
        builder.append("]");
        System.out.println(builder.toString());
    }

    public void displayFromTail() {
        Node current = tail;
        StringBuilder builder = new StringBuilder();
        builder.append("尾---->头：[");
        while (current.pre != null) {
            builder.append(current.data.toString() + "->");
            current = current.pre;
        }
        builder.append(current.data.toString());
        builder.append("]");
        System.out.println(builder.toString());
    }

    public class Node {
        private Object data;

        private Node pre;

        private Node next;

        public Node(Object data) {
            this.data = data;
            this.pre = null;
            this.next = null;
        }
    }
}