Copy List Nodes with Next and Arbitrary Random Links

### Problem Deep-copy a linked list whose nodes contain `val`, `next`, and `random`. A random link can point to any node in the list, including itself, or to null. Return the new head. Create exactly one new node per original node and preserve both kinds of links through the corresponding new nodes. No pointer in the copy may refer to an original node. ```cpp Node* copyRandomList(Node* head); ``` The function receives only the original custom-node head. Display pairs `[value,randomIndex]` use zero-based indices along the next chain; they are not array arguments. ### Examples ```text Original display: [[5,1],[5,0]] Copy display: [[5,1],[5,0]] ``` The equal-valued nodes are distinct, and the new random links point to their new counterparts. ```text Original display: [[-2,0]] Copy display: [[-2,0]] ``` ### Constraints - There are between 0 and 1000 nodes. - Values lie between -10000 and 10000, inclusive. - Every random pointer is null or refers to a node in the original list.