https://leetcode.com/problems/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.
Detailed description of the best solution. Picture in the comments helps to understand the algorithm very much. https://leetcode.com/problems/copy-list-with-random-pointer/discuss/43491/A-solution-with-constant-space-complexity-O(1)-and-linear-time-complexity-O(N)