I got the hash map version out pretty cleanly.
Start by clarifying the problem and edge cases, then present the hash map solution with O(n) time and space, explaining how it maps original nodes to copies. Next, describe the interleaving approach: first insert copies after each original, then set random pointers, and finally separate the lists to achieve O(1) extra space. Compare trade-offs and discuss when each approach is preferable.
Pro tip: Mention that the interleaving approach modifies the original list temporarily but restores it, so it's safe if the original list must remain unchanged. Also, note that the hash map solution is simpler and less error-prone, so it's often preferred in practice unless memory is extremely constrained.
Ask about input constraints, whether the original list can be modified, and handle edge cases like empty list, single node, or cycles.
Explain creating a mapping from original nodes to their copies, then setting next and random pointers using the map. Analyze time and space complexity.
Describe inserting a copy after each original node, then setting random pointers for copies using the original's random pointer, and finally separating the two lists.
Discuss when to use each approach: hash map for simplicity and when extra space is acceptable; interleaving for O(1) space but with temporary modification.
Walk through a small example to verify correctness, ensuring random pointers are correctly set and the original list is restored.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.