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。

    示例 1：
    输入：head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
    输出：[[7,null],[13,0],[11,4],[10,2],[1,0]]

    示例 2：
    输入：head = [[1,1],[2,1]]
    输出：[[1,1],[2,1]]

    示例 3：
    输入：head = [[3,null],[3,0],[3,null]]
    输出：[[3,null],[3,0],[3,null]]

    示例 4：
    输入：head = []
    输出：[]
    解释：给定的链表为空（空指针），因此返回 null。

    1. """
    2. # Definition for a Node.
    3. class Node:
    4.     def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):
    5.         self.val = int(x)
    6.         self.next = next
    7.         self.random = random
    8. """
    10. class Solution:
    11.     def copyRandomList(self, head: 'Optional[Node]') -> 'Optional[Node]':
    12.         # if head is None:
    13.         #     return None
    14.         # cur = head
    15.         # next = None
    16.         # while cur is not None:  # 1 -> 2 变化成 1 -> 1' -> 2 -> 2'
    17.         #     next = cur.next
    18.         #     cur.next = Node(cur.val)
    19.         #     cur.next.next = next
    20.         #     cur = next
    21.         # cur = head
    22.         # curcopy = None
    23.         # while cur is not None:  # 一对一对取出来连random指针
    24.         #     next = cur.next.next
    25.         #     curcopy = cur.next
    26.         #     curcopy.random = cur.random.next if cur.random is not None else None
    27.         #     cur = next
    28.         # res = head.next
    29.         # cur = head
    30.         # while cur is not None:  # 分离链表
    31.         #     next = cur.next.next
    32.         #     curcopy = cur.next
    33.         #     cur.next = next
    34.         #     curcopy.next = next.next if next is not None else None
    35.         #     cur = next
    36.         # return res
    37.         hashmap = dict()
    38.         cur = head
    39.         while cur is not None:
    40.             hashmap[cur] = Node(cur.val)
    41.             cur = cur.next
    42.         cur = head
    43.         while cur is not None:
    44.             hashmap.get(cur).next = hashmap.get(cur.next)
    45.             hashmap.get(cur).random = hashmap.get(cur.random)
    46.             cur = cur.next
    47.         return hashmap.get(head)
    1. class Solution:
    2.     def copyRandomList(self, head: 'Optional[Node]') -> 'Optional[Node]':
    3.         if head is None:
    4.             return None
    5.         cur = head
    6.         next = None
    7.         while cur is not None:  # 1 -> 2 变化成 1 -> 1' -> 2 -> 2'
    8.             next = cur.next
    9.             cur.next = Node(cur.val)
    10.             cur.next.next = next
    11.             cur = next
    12.         cur = head
    13.         curcopy = None
    14.         while cur is not None:  # 一对一对取出来连random指针
    15.             next = cur.next.next
    16.             curcopy = cur.next
    17.             curcopy.random = cur.random.next if cur.random is not None else None
    18.             cur = next
    19.         res = head.next
    20.         cur = head
    21.         while cur is not None:  # 分离链表
    22.             next = cur.next.next
    23.             curcopy = cur.next
    24.             cur.next = next
    25.             curcopy.next = next.next if next is not None else None
    26.             cur = next
    27.         return res