138. Copy List with Random Pointer

题目：

138. Copy List with Random Pointer

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

The Linked List is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

• val: an integer representing Node.val
• random_index: the index of the node (range from 0 to n-1) where random pointer points to, or null if it does not point to any node.

Example 1:

Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]

Example 3:

Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]

Example 4:

Input: head = []
Output: []
Explanation: Given linked list is empty (null pointer), so return null.

Constraints:

• -10000 <= Node.val <= 10000
• Node.random is null or pointing to a node in the linked list.
• Number of Nodes will not exceed 1000.

138. 复制带随机指针的链表

给定一个链表，每个节点包含一个额外增加的随机指针，该指针可以指向链表中的任何节点或空节点。

要求返回这个链表的 深拷贝。

我们用一个由 n 个节点组成的链表来表示输入/输出中的链表。每个节点用一个 [val, random_index] 表示：

• val：一个表示 Node.val 的整数。
• random_index：随机指针指向的节点索引（范围从 0 到 n-1）；如果不指向任何节点，则为 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。

提示：

• -10000 <= Node.val <= 10000
• Node.random 为空（null）或指向链表中的节点。
  节点数目不超过 1000 。

思路：

方法1：

Hashmap字典映射

方法2:

1. 新节点连接到原始节点（node1->node1'->node2->node2'）
2. 新节点random指针赋值
3. 拆分新旧链表

代码：

class Solution:
    def copyRandomList(self, head: Node) -> Node:
        from collections import defaultdict
        d = defaultdict(lambda: Node(0))
        d[None] = None
        current = head
        while current:
            d[current].val = current.val
            d[current].next = d[current.next]
            d[current].random = d[current.random]
            current = current.next
        return d[head]

    def copyRandomListV01(self, head: Node) -> Node:
        d = {}
        current = head
        while current:
            d[current] = Node(current.val)
            current = current.next

        current = head

        while current:
            d[current].next = d.get(current.next, None)
            d[current].random = d.get(current.random, None)
            current = current.next

        return d[head]

    def copyRandomListV02(self, head: Node) -> Node:
        current = head
        while current:
            node = Node(current.val)
            node.next = current.next
            current.next = node
            current = node.next

        current = head
        while current:
            current.next.random = current.random and current.random.next
            current = current.next.next

        second = head.next
        current = head.next
        while current.next:
            head.next = current.next
            head = current.next
            current.next = head.next
            current = current.next
        head.next = None
        return second