How do you sort a linked list in O(n log n) time and O(1) extra memory?
PICTURE THIS: GIT FLOW
Simple meaning
Bottom-up merge sort: split with slow/fast, merge sorted runs of size 1, 2, 4, ...
WHY — Linked List instead of guessing?
Why interviewers care about Linked List:
question about Linked List.
trade-offs, and what you would actually do on a DSA project - not buzzwords.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Bottom-up merge sort: split
with slow/fast, merge sorted runs of size 1, 2, 4, ...
- 2Why it exists
using pointer rewires.
- 3Time is O(n log
n) and extra space is O(1) besides recursion-free iteration.
- 4Recursion top-down is O(log
n) stack, which some interviewers reject.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Bottom-up merge sort: split with slow/fast, merge sorted runs of size 1, 2, 4, ... using pointer rewires.