剑指 Offer 35. 复杂链表的复制

请实现 copyRandomList 函数，复制一个复杂链表。在复杂链表中，每个节点除了有一个 next 指针指向下一个节点，还有一个 random 指针指向链表中的任意节点或者 null。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/fu-za-lian-biao-de-fu-zhi-lcof
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

class Solution {
    public Node copyRandomList(Node head) {
        if (head == null) {
            return null;
        }
        Node cur = head, next, copy;
        while (cur != null) {
            next = cur.next;
            copy = new Node(cur.val);
            cur.next = copy;
            copy.next = next;
            cur = next;
        }

        cur = head;

        while (cur != null) {
            next = cur.next.next;
            copy = cur.next;
            if (cur.random != null) {
                copy.random = cur.random.next;
            }
            cur = next;
        }

        Node copyHead = head.next;
        cur = head;
        while (cur != null) {
            next = cur.next.next;
            copy = cur.next;
            cur.next = next;
            copy.next = next == null ? null : next.next;
            cur = next;
        }

        return copyHead;
    }
}

class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}