Copy List with Random Pointer

Copy List with Random Pointer is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Graph Traversal Patterns (DFS & BFS) pattern, in the Deep Copy / Cloning subpattern.

Problem statement

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 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, randomindex] where: val: an integer representing Node.val randomindex: 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.

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: The given linked list is empty (null pointer), so return null.

Constraints: 0 <= n <= 1000 -10000 <= Node.val <= 10000 Node.random is null or is pointing to some node in the linked list.

Topics and companies

Topics: Hash Table, Linked List.

Reported in interviews at Amazon, Facebook, Microsoft, Bloomberg, eBay, Oracle, Yahoo, Qualtrics.

How to practise Copy List with Random Pointer on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript, Kotlin, PHP, Python, python3, Ruby, Scala, Swift and TypeScript. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(n) time and O(1) space.

Open Copy List with Random Pointer in the code editor, or read the Copy List with Random Pointer editorial for a worked solution with its approach and complexity analysis.

Where Copy List with Random Pointer sits in the DSA pattern sheet

Problems related to Copy List with Random Pointer

Other problems that use the same Deep Copy / Cloning and Graph Traversal Patterns (DFS & BFS) techniques:

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