Practice: Reverse Linked List

Problem: https://leetcode.com/problems/reverse-linked-list/

Recognition reminder: you are flipping the direction of every link in a chain of nodes, in place, with no index access. That is the in-place reversal primitive, the single most reused move of the week.

Before you start (the five-beat rhythm)

  1. Your Pattern Card for this week is already written.
  2. Name the pattern aloud and write your approach as a plain-English comment before any code.
  3. Struggle floor: 25 minutes unaided. No hints, no AI, no Discuss tab.
  4. If stuck past the floor, ask the tutor for a hint. Six rungs, one per ask.
  5. Debrief in your commit message before moving to the next problem.

Your target

Fill these in yourself before you look at anyone else’s solution:

Target time complexity:  ____
Target space complexity: ____

There is an iterative version and a recursive version. Find the iterative one first; then ask what the recursive version costs in space that the iterative one does not.

Where your code goes

Write your solution in your own work repo (see getting-started.md), not in this folder. Your solution.py must define the same ListNode class LeetCode gives you (val, next) and a function reverse_list(head) that returns the new head. This folder ships only the problem spec and a provided-example test (tests/test_provided.py) so you can check the given cases locally before you submit to LeetCode’s judge. The judge is the oracle; the tutor will not confirm your answer by reading it.

Debrief (paste into your commit message) 

1. What pattern did this turn out to be?
2. What was the trigger phrase or input shape that should have made me reach for it?
3. What was the time and space complexity, and what would dominate at scale?
4. What edge case would have broken my first attempt?
5. What would I do differently in three days when I see this cold?