Build a LeetCode Notes System That Becomes Your Personal Knowledge Base

Why Ad-Hoc Notes Don’t Stick

Copy-pasting full solutions into random docs doesn’t build recall. You need a structured note system that captures triggers, pitfalls, and patterns—short enough to review, rich enough to reuse for interviews. Notes should help you recreate the solution in minutes, not become a code archive you never read.

The cognitive science angle

• Generation effect: Writing the idea yourself boosts recall more than copy-paste.
• Retrieval practice: Recalling key steps (trigger → pattern → pitfall) cements memory.
• Chunking: Grouping by pattern reduces cognitive load; you recall “sliding window” as a unit.
• Spaced repetition: Brief, timed reviews beat marathon rereads.

The Lightweight Notes Template

Core fields (keep it skimmable)

• Trigger: The phrase that hinted at the pattern (e.g., “longest substring without repeats” → sliding window).
• Pitfall: The exact place you got stuck (e.g., “forgot to shrink window before updating result”).
• Pattern: Sliding window, BFS, binary search, etc.
• Complexity: Time/space in one line.
• Edge Cases: 3–5 bullet tests.
• Follow-up: One variation you’d expect in interviews.

Example entry (concise)

Problem: LC 3 Longest Substring Without Repeating Characters
Trigger: “Longest substring” + “no repeats” ⇒ sliding window
Pitfall: Didn't shrink window before updating result
Pattern: Sliding window (set)
Complexity: O(N) time, O(K) space (unique chars)
Edge cases: "", "aaaa", "abba", "abcabcbb"
Follow-up: What changes for k repeating allowed? (use freq map + counter)

Pseudo-Code to Anchor the Idea

Anchoring notes with a few lines of pseudo-code cements the pattern:

function longestSubstringNoRepeat(s: string): number {
  const seen = new Set<string>();
  let left = 0, best = 0;
  for (let right = 0; right < s.length; right++) {
    while (seen.has(s[right])) {
      seen.delete(s[left]);
      left++;
    }
    seen.add(s[right]);
    best = Math.max(best, right - left + 1);
  }
  return best;
}

Keep code short; the goal is to remind yourself of the pattern, not archive every line.

Folder Structure That Scales

• Use Markdown files named YYYY-MM-DD-pattern-problem.md.
• Create folders by pattern: notes/sliding-window, notes/graph-bfs, notes/dp.
• Add an index file per folder linking to entries (like a lightweight coding interview guide).
• Keep language-specific snippets in subfolders (js, py, cpp) if you multi-track.

Tagging That Actually Helps

• Tag by pattern, difficulty, status (learned/review), and language.
• Add 2–3 “related problems” links per note to build a graph; these internal links mirror spaced repetition.
• Mark “must review” items when you needed multiple hints.

Spaced Repetition Schedule (Minimalist)

• Day 0: Write note after solving.
• Day 3: Re-solve from memory.
• Day 7: Quick skim + one edge-case test.
• Day 30: Mock interview explanation + timeboxed 10-minute solve.
  This entire cycle adds ~15–20 minutes spread over a month but dramatically improves retention.

Worked Example: Turning One Solve Into a Knowledge Asset

1. Solve “Course Schedule” (topological sort).
2. Write trigger: “detect cycle in prerequisites” ⇒ graph + indegree + queue.
3. Pitfall: Forgot to initialize indegree for isolated nodes.
4. Pattern: Kahn’s algorithm (BFS).
5. Complexity: O(V+E).
6. Edge cases: isolated node, multiple components, self-loop, long chain.
7. Follow-up: “How would you return a valid ordering?” (Keep ordering list).
8. Link to related: “Alien Dictionary,” “Minimum Height Trees.”
9. Add to DSA learning path under Graphs → Toposort.

How to Capture Mistakes So They Don’t Repeat

• Write a “bug diary” line: Bug → Cause → Guardrail.
  • Example: “Window never shrank → forgot to move left before updating answer → Always shrink first, then update.”
• Add a quick assert or invariant you’ll reuse: “window contains unique chars,” “heap size ≤ k.”
• Note the test that exposed it; reuse that test on future similar problems.

Template for Fast Reviews

When time is short, review like this:

• Read Trigger → say the Pattern out loud.
• Recall Pitfall → say the Guardrail.
• Glance at complexity → verify it still makes sense.
• Pick one edge case → mentally trace 3 steps of the algorithm.
  This takes 60–90 seconds per note and compounds over weeks.

Multi-Language Notes Without Chaos

• Keep one “primary” language per note. If you add a second, tuck it below a divider.
• Focus on idioms: Python list slices, Java Deque, C++ vector vs. array, TypeScript types.
• Avoid duplicating the whole solution; capture only syntax gotchas that matter for that pattern.

Turning Notes Into Interview Stories

• For each pattern, write a 3-sentence story: problem, constraint, and trade-off.
  • “We needed shortest path on an unweighted grid → BFS → O(V+E) → watch for visited early.”
• Record one trade-off per note: “Used set for O(1) membership; could use array[256] for ASCII to cut allocations.”
• Add an “explain like I’m in an interview” blurb to practice phrasing.

Using AI Without Losing Ownership

Tools like LeetCopilot can auto-capture the trigger, pitfall, and complexity after each solve, then slot them into a step-by-step hinting system for future refreshers. Use AI to generate edge cases or summarize your code, but keep ownership of the final note—interviewers want your words, not boilerplate. A light mock interview simulator pass can also test whether your notes are clear enough to speak from.

Linking Notes to a Practice Rhythm

• Before each session, open yesterday’s note and re-solve in 5 minutes.
• After each session, link the new note to two older ones by pattern.
• Each Friday, add one “stretch” link: a harder variant you’ll tackle next week.
• Each month, prune or merge redundant notes; keep only the clearest version.

Common Pitfalls in Note-Taking

• Writing essays; if you can’t review it in 90 seconds, it’s too long.
• Skipping edge cases; that’s where most interview bugs live.
• Storing notes without tags; untagged notes are invisible when you need them.
• Mixing languages in one entry; keep one language per note for clarity.
• Copying discussion solutions verbatim; you retain little without paraphrasing.

Example of a Full Note (DP Variant)

Problem: LC 198 House Robber
Trigger: “Max sum without adjacent” ⇒ DP on linear array
Pitfall: Forgot base case for n=1
Pattern: 1D DP (choose/skip)
Complexity: O(N) time, O(1) space (rolling)
Recurrence: dp[i] = max(dp[i-1], dp[i-2] + nums[i])
Edge cases: [], [5], [2,1,1,2], [100,1,1,100]
Follow-up: Circular variant? Use two passes (exclude first, exclude last)
Related: LC 213, LC 740 (Delete and Earn)
Trade-off: Rolling array to cut space; clarity vs. readability for interviews

Minimal Automation That Helps (Without Becoming a Distraction)

• A script to stamp new files with the template.
• Snippets for common patterns (window, BFS, DP).
• A simple search (ripgrep) to find all notes with “overflow” or “visited” mistakes.
• Back up notes to git; small diffs keep you honest about what changed.

Weekly Maintenance in 20 Minutes

• 5 minutes: Tag new notes and link related ones.
• 10 minutes: Re-solve two problems from notes marked “review.”
• 5 minutes: Write one “bug diary” entry summarizing the week’s recurring pitfall.

FAQ

How many details should I include per note?
Just enough to recreate the solution in under two minutes: trigger, pitfall, pattern, complexity, and 3–5 edge cases.

Should I store full code?
Keep a short, idiomatic snippet. The rest can live in your IDE; the note is for memory cues, not archives.

How do I review efficiently?
Filter by tag (e.g., “graph bfs”) and run a 10-minute blitz: read triggers, say the approach out loud, then solve one small case.

Can AI write my notes for me?
Let AI draft, but edit heavily. Your own wording is what you’ll recall fastest in interviews.

How do I keep this lightweight long-term?
Standardize filenames, reuse the same template, and cap notes at ~8 bullet lines. Consistency beats complexity.

What if I learn in two languages?
Keep one primary language per note and add a short “other language” snippet only for syntax pitfalls; don’t duplicate everything.

Conclusion

A good LeetCode notes system is compact, tagged, and reviewable. Capture triggers, pitfalls, patterns, and edge cases; revisit them on a cadence; and keep one code cue per entry. With a disciplined template—and a bit of AI assistance to handle the busywork—you’ll turn every solved problem into an interview-ready asset that compounds over time.