138.复制带随机指针的链表

https://leetcode-cn.com/problems/copy-list-with-random-pointer/submissions/

 public Node copyRandomList(Node head) {
        if (head == null) return null;
        Node cur = head;
        Node next = null;
        while (cur != null) {
            next = cur.next;
            cur.next = new Node(cur.val);
            cur.next.next = next;
            cur = next;
        }
        cur = head;
        while (cur != null) {
            next = cur.next.next;
            cur.next.random = cur.random == null ? null : cur.random.next;
            cur = next;
        }
        Node ans = head.next;
        cur = head;
        while (cur != null) {
            next = cur.next.next;
            cur.next.next = next == null ? null : next.next;
            cur.next = next;
            cur = next;
        }
        return ans;
    }