双向链表

class Node {//该节点省略data域
    public int no;
    public Node next;
    public Node pre;

    public Node(int no) {
        if (no >= 0) {//要求no要大于0
            this.no = no;
        }
    }

    @Override
    public String toString() {
        return "Node{" +
                "no=" + no +
                '}';
    }
}

public class DoubleLinkedList {
    Node head = new Node(0);

    public void add(Node node) {//节点加入链表尾
        Node temp = head;
        while (true) {
            if (temp.no == node.no) {//该编号节点已存在
                return;
            } else if (temp.next == null) {
                break;
            }
            temp = temp.next;
        }
        temp.next = node;
        node.pre = temp;
    }

    public void addByOrder(Node node) {//根据节点编号升序加入
        Node temp = head;
        while (true) {
            if (temp.no == node.no) {//该编号节点已存在
                return;
            } else if (temp.next == null) {//加入链尾
                break;
            } else if (temp.next.no > node.no) {//插入第一个编号比node大节点的前一位
                temp.next.pre = node;
                node.next = temp.next;
                break;
            }
            temp = temp.next;
        }
        temp.next = node;
        node.pre = temp;
    }

    public void update(Node node) {//更新节点
        Node temp = head.next;
        while (true) {
            if (temp == null) {//该编号节点不存在
                return;
            } else if (temp.no == node.no) {//找到该编号节点
                if (temp.next != null) {
                    temp.next.pre = node;
                    node.next = temp.next;
                }
                temp.pre.next = node;
                node.pre = temp.pre;
                return;
            }
            temp = temp.next;
        }
    }

    public void delete(int no) {
        Node temp = head.next;
        while (true) {
            if (temp == null) {//该编号节点不存在
                return;
            }
            if (temp.no == no) {//被跳过的节点没有引用，被回收
                temp.pre.next = temp.next;
                if (temp.next != null) {//防止要删除的节点在链尾
                    temp.next.pre = temp.pre;
                }
                return;
            }
            temp = temp.next;
        }
    }

    public void show() {//打印链表
        Node temp = head.next;
        while (true) {
            if (temp == null) {
                return;
            }
            System.out.println(temp);
            temp = temp.next;
        }
    }

    public int getLength() {//获取链表有效节点个数
        int length = 0;
        Node temp = head.next;
        while (temp != null) {
            length++;
            temp = temp.next;
        }
        return length;
    }

    //用一条空的单向链表调用，传入两条待合并单向链表各自的第一个有效节点
    public void merge(Node n1, Node n2) {
        Node cur = head;
        while (n1 != null && n2 != null) {
            if (n1.no <= n2.no) {
                cur.next = n1;
                n1.pre = cur;
                n1 = n1.next;
            } else {//n1.no > n2.no
                cur.next = n2;
                n2.pre = cur;
                n2 = n2.next;
            }
            cur = cur.next;
        }
        //若n1全部比较合并后，n2剩余节点加入链尾；反之亦然
        if (n1 == null) {
            cur.next = n2;
            n2.pre = cur;
        } else {
            cur.next = n1;
            n1.pre = cur;
        }
    }
}