Practice: Longest Substring Without Repeating Characters

Problem: https://leetcode.com/problems/longest-substring-without-repeating-characters/

Recognition reminder: you want the longest contiguous run of characters with no repeats. That is the archetypal variable window: expand the right end to take in more, and shrink the left end whenever a repeat enters, so the window stays all-distinct.

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: ____

Decide what the window state is: what do you store so you know, in O(1), whether the incoming character is already inside the window? The space target depends on the alphabet, so state it in terms of the number of distinct characters.

Where your code goes

Write your solution in your own work repo (see getting-started.md), not in this folder. 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?