138.Copy List with Random Pointer
===

###### tags: `Medium` `Linked List` `Hash Table`

[138. Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer/)

### 題目描述

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

Construct a [deep copy](https://en.wikipedia.org/wiki/Object_copying#Deep_copy) of the list. The deep copy should consist of exactly `n` **brand new** nodes, where each new node has its value set to the value of its corresponding original node. Both the `next` and `random` pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. **None of the pointers in the new list should point to nodes in the original list**.

For example, if there are two nodes `X` and `Y` in the original list, where `X.random --> Y`, then for the corresponding two nodes `x` and `y` in the copied list, `x.random --> y`.

Return *the head of the copied linked 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`) that the `random` pointer points to, or `null` if it does not point to any node.

Your code will **only** be given the `head` of the original linked list.

### 範例

**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]]

**Constraints**:

* 0 <= `n` <= 1000
* -10^4^ <= `Node.val` <= 10^4^
* `Node.random` is `null` or is pointing to some node in the linked list.

### 解答

### Reference

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