Practice: Merge Two Sorted Lists

Problem: https://leetcode.com/problems/merge-two-sorted-lists/

Recognition reminder: you are combining two already-sorted chains into one sorted chain by repeatedly attaching the smaller head. That is the merge primitive, and it is the cleanest possible use of the dummy head.

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: ____

A dummy head removes the “which list is the first node” special case. When one list runs out, think about why you can attach the entire remainder of the other list in a single step instead of node by node.

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 merge_two_lists(list1, list2) that returns the head of the merged list. 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?