LeetCode Practice

Solve LeetCode in your editor. Track progress. Run timed interviews.

A VS Code and Cursor extension with problem browsing, template generation, inline example runners, XP and streak tracking, and timed interview workflows — with optional cloud sync.

Every save now surfaces four layers of inline feedback as ghost text on the relevant line: interview anti-pattern lint, a constraint-aware complexity budget (🟢/🟡/🔴), adversarial edge-case probes, and live example results. No popups; hover any decoration to read details or click "turn off" for that feature.

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Install

• VS Code — Install from Marketplace, or in the command palette:

  ext install NikkyAmresh.leetcode-practice
  

• Cursor, VSCodium, and other OSS editors — Install from Open VSX

The extension activates automatically when a workspace contains a .leetcode file.

Quick Start

1. Open a folder in VS Code or Cursor.
2. Create a .leetcode file in the workspace root (an empty {} is enough).
3. Run LeetCode: Sign In from the command palette.
4. Open the LeetCode sidebar and pick a problem.
5. Click Create File, solve, then run with LeetCode: Run Examples or Ctrl/Cmd+Shift+R.

Features

• Browse and solve — Full problemset, study plans, curated problem lists, and Question of the Day in sidebar views. Rich problem webview with "Create File" in TypeScript, JavaScript, Python, C++, or Java.
• Companies sidebar — Browse problems grouped by 463 companies with per-company frequency, global acceptance rate, color-coded difficulty dots, and topics in the row tooltip. Click to open in the editor. Topics + companies are also surfaced inside the problem webview as collapsible chips. Toggle via leetcodePractice.showCompanies.
• Inline feedback on save — Every save runs all enabled features at once, rendered as ghost text on the relevant line with a trusted-markdown hover and a one-click "turn off" link per feature. No popups.
  • Interview anti-pattern lint — flags mutate-input, built-in .sort() on sorting problems, magic numbers (26 / 128 / 1000000007), and indented debug print/console.log/System.out.println across py/ts/js/cpp/java. Emits a real VS Code diagnostic (squiggle + Problems panel) and an inline hint. Suppressible per line with // lcex-lint-ignore: <rule>.
  • Complexity budget — parses the problem's Constraints: section, derives a target Big-O from the largest size cap, estimates loop nesting by indent, and paints 🟢 / 🟡 / 🔴 on the function signature plus a nest k× → O(nᵏ) badge on each loop.
  • Adversarial edge-case probes — turns parsed constraints into candidate edge cases (empty, single, max-size, boundary values, negatives, zeros, charset / sorted / distinct flags) and surfaces them inline on the signature. Advisory in this release.
  • Run examples on save — parses // Expected: / # expected: comments and diffs against console.log / print output; results render inline as ✓ or ✗ expected X · got Y with a dedicated timeout message for >15s runs. Also available on-demand.
• Run in terminal — Execute the current solution file end-to-end in the integrated terminal.
• Progress tracking — Solved / attempting / cleared states, daily streaks, XP and levels, daily goals, and a stats dashboard with trends.
• Interview mode — Ad-hoc timed sessions (45 / 60 / 180 min) or planned .lcInterview mocks. Focus layout hides hints; each attempt produces a .lcireport snapshot.
• Solution notes and agent actions — Capture notes in .hint files; trigger Make Runnable, Hint, and Explain My Code from the editor. The Hint action writes a JSON sidecar (~/.lcex/hint-context/<slug>.json) with the static complexity estimate, parsed problem-size budget, verdict, and top hotspot, so the lcex-dsa-hint skill tailors the nudge to what you actually wrote.
• DSA practice loop (opt-in, all off by default) — Five features that go beyond "did your sample pass?":
  • Spaced-repetition bug review (leetcodePractice.bugReview.enabled) — failing examples are snapshotted to ~/.lcex/bug-reviews.json and resurface as re-attempt drills 3 / 7 / 30 / 90 days later; status bar shows N reviews due.
  • Differential fuzzer (leetcodePractice.fuzzer.enabled) — define bruteForce + fuzzInputs(seed) alongside your solution; the fuzzer reports the first divergence as a counterexample (and snapshots it to the SR queue if bug-review is on).
  • Empirical complexity fitter (leetcodePractice.empiricalFit.enabled) — define benchmark(n); the fitter times your solution at growing N, fits eight candidate curves, and flags when empirical complexity exceeds the static estimate.
  • Recursion call-tree visualizer (leetcodePractice.recursionTree.enabled) — define traceCall(); the visualizer instruments your recursive function and renders the live call tree with memo-hit edges (the exact cells memoization would skip).
  • Iterative traversal visualizer (leetcodePractice.iterativeVisualizer.enabled) — wrap your stack/queue with lcexTrace.track(container, "stack"|"queue") (or lcex_trace.track(...) in Python) inside traceCall(); the harness records every push/pop and renders the DFS/BFS traversal tree with revisit edges (cycles, redundant work).
  • TS / JS / Python today; C++ is phase-2.
• Workspace config editor — Custom editor for .leetcode files makes study plan, problem list, language, and file-naming overrides a UI action.
• Cloud sync (optional) — Sign in with Google to push and pull stats across machines via Firebase. Fully optional; the extension works offline without it.

Screenshots

.leetcode config editor	Problem view + run in terminal
.lcInterview plan editor	.lcireport interview report
Stats overview	Minutes and solved trends
Daily time and solved breakdown	Solution notes with hint and analyze

Commands

All commands are available under the LeetCode category in the command palette.

Problems

Command	Description
LeetCode: Open/Create Problem	Open a problem and create its solution file
LeetCode: Open Question of the Day	Jump straight to today's QOTD
LeetCode: Refresh Problems	Re-fetch the problemset cache
LeetCode: Search Companies	Filter the Companies view by company / problem / topic
LeetCode: Filter Companies by Difficulty	Restrict the Companies view to Easy / Medium / Hard
LeetCode: Refresh Companies	Reload the bundled companies dataset
LeetCode: Sign In / Sign Out	Manage the LeetCode session cookie

Running

Command	Shortcut	Description
LeetCode: Run Examples	—	Parse // Expected: comments and diff results inline
LeetCode: Run in Terminal	Ctrl/Cmd+Shift+R	Execute the current solution file

Inline feedback

Command	Shortcut	Description
LeetCode: Lint Solution for Interview Anti-Patterns	—	Run the lint rules on demand
LeetCode: Show Complexity Budget vs. Estimate	—	Parse constraints, estimate your Big-O, paint the verdict
LeetCode: Surface Adversarial Edge Cases	—	Inline hint with candidate edge cases
LeetCode: Clear Inline Decorations	Ctrl/Cmd+K Ctrl/Cmd+L	Wipe all lcex ghost text from the active editor
LeetCode: Toggle Interview Lint on Save	—	Flip leetcodePractice.lint.enabled
LeetCode: Toggle Complexity Budget on Save	—	Flip leetcodePractice.complexityBudget.enabled
LeetCode: Toggle Edge-Case Probes on Save	—	Flip leetcodePractice.adversarialTests.enabled
LeetCode: Toggle Run Examples on Save	—	Flip leetcodePractice.runExamplesOnSave.enabled
LeetCode: Toggle All Inline Decorations	—	Master kill switch for every lcex decoration

DSA practice loop (opt-in)

Command	Description
LeetCode: Open Next Bug Review	Opens the next due failing example as a re-attempt drill (leetcodePractice.bugReview.enabled)
LeetCode: Fuzz vs Brute Force	Runs bruteForce + fuzzInputs(seed) against your solution, reports the first divergence (leetcodePractice.fuzzer.enabled)
LeetCode: Measure Complexity (Empirical)	Times benchmark(n) at growing N, fits a curve, flags when empirical class exceeds static estimate (leetcodePractice.empiricalFit.enabled)
LeetCode: Visualize Recursion Call Tree	Instruments the recursive function in the open file (TS/JS/Python) and renders the call tree with memo-hit edges (leetcodePractice.recursionTree.enabled)
LeetCode: Visualize Iterative Traversal	Wraps a user-tracked stack/queue (lcexTrace.track(...)) and renders the DFS/BFS traversal tree with revisit edges (leetcodePractice.iterativeVisualizer.enabled)

Interview

Command	Description
LeetCode: Interview Mode — Start / Stop	Run an ad-hoc timed session
LeetCode: Generate LC Interview (AI)	Scaffold a planned .lcInterview
LeetCode: Open LC Interview Report…	Browse .lcireport history

Stats and goals

Command	Description
LeetCode: View Stats	Open the stats dashboard
LeetCode: Set Daily Goal	Configure daily problem / minute targets

Cloud sync

Command	Description
LeetCode: Sign in to Cloud Sync / Sign out of Cloud Sync	Manage Firebase session
LeetCode: Set LeetCode username	Link your LeetCode handle
LeetCode: Push stats to cloud now / Pull stats from cloud	Manual sync

Privacy

Command	Description
LeetCode: Toggle anonymous analytics	Opt in or out of anonymous usage analytics

Extension Settings

Setting	Description
leetcodePractice.defaultDirectory	Where new solution files are created
leetcodePractice.fileNamePattern	id (e.g. 1.ts) or slug (e.g. two-sum.ts)
leetcodePractice.language	typescript, javascript, python, cpp, or java
leetcodePractice.problemViewMode	Layout for the problem webview
leetcodePractice.suppressAiTabOnSolve	Don't reopen AI tab after marking solved
leetcodePractice.suppressAiTabWorkspaceWide	Workspace-wide version of the above
leetcodePractice.internalApiUrl	Use a custom backend instead of LeetCode's GraphQL
leetcodePractice.activeStudyPlan	Currently active study plan slug
leetcodePractice.activeProblemList	Currently active problem list slug
leetcodePractice.studyPlans	Study plans to show in the sidebar
leetcodePractice.problemLists	Curated problem lists to show in the sidebar
leetcodePractice.showProblemLists	Toggle the problem lists view
leetcodePractice.showContests	Toggle the Practice Past Contests view
leetcodePractice.showCompanies	Toggle the Companies view (default: on)
leetcodePractice.leetcodeUsername	LeetCode username for cloud sync
leetcodePractice.analytics.enabled	Send anonymous usage analytics (default: on)
leetcodePractice.inlineDecorations.enabled	Master switch for all lcex inline ghost text (default: on)
leetcodePractice.lint.enabled	Run interview anti-pattern lint on save (default: on)
leetcodePractice.complexityBudget.enabled	Derive target Big-O from constraints and paint 🟢/🟡/🔴 on save (default: on)
leetcodePractice.adversarialTests.enabled	Surface edge-case probes on save (default: off — run LeetCode: Surface Adversarial Edge Cases on demand)
leetcodePractice.runExamplesOnSave.enabled	Run example lines automatically on save (default: on)
leetcodePractice.runExamples.sandbox	Sandbox solution execution: auto (sandbox on macOS, normal elsewhere), sandbox (force), off (default: auto)
leetcodePractice.bugReview.enabled	Spaced-repetition queue of failed examples; resurfaces 3/7/30/90 days later (default: off)
leetcodePractice.fuzzer.enabled	Differential fuzzer vs bruteForce + fuzzInputs(seed) (default: off)
leetcodePractice.empiricalFit.enabled	Empirical complexity fitter; needs benchmark(n) (default: off)
leetcodePractice.recursionTree.enabled	Recursion call-tree visualizer; needs traceCall() (default: off)
leetcodePractice.iterativeVisualizer.enabled	Iterative traversal visualizer; needs lcexTrace.track(container) inside traceCall() (default: off)

Privacy & anonymous analytics

The extension can send anonymous, bucketed usage analytics to Firebase to help prioritise which features to improve. This is opt-outable at any time.

What is sent:

• A pseudonymous per-install UUID (generated on first launch, never linked to your identity).
• Which feature you used (e.g. run_examples, interview_start, agent_hint).
• Where it was triggered (command palette, sidebar, webview…).
• Coarse dimensions: language bucket (ts/js/py/cpp/java), difficulty bucket (E/M/H), duration bucket (0_5m / 5_15m / 15_60m / 60m+), count bucket.
• Extension version, VS Code version, OS platform, locale, local hour of day.

What is never sent:

• Your uid, email, LeetCode username, or session cookie.
• Problem slugs, titles, descriptions, notes, or any code.
• File paths, workspace names, or folder names.
• Exact timestamps, error messages, stack traces.

How it's protected:

• Analytics events live in a separate Firestore collection (/logs). Security rules restrict reads to a single admin uid — no user, including you, can read logs back. Writes are strictly schema-validated: only enum values from an allow-list are accepted.
• Requires sign-in to cloud sync. If you're not signed in, nothing is sent.
• Respects the VS Code telemetry.telemetryLevel setting. If VS Code telemetry is off, analytics is off too.

Opt out:

• Run LeetCode: Toggle anonymous analytics, or
• Set leetcodePractice.analytics.enabled to false in settings, or
• Set VS Code's telemetry.telemetryLevel to off.

Workspace Config (.leetcode)

Any setting above can be overridden per-workspace in the .leetcode file. Workspace values take precedence over user settings.

{
  "studyPlans": [{ "slug": "top-interview-150", "name": "Top Interview 150" }],
  "problemLists": [{ "slug": "graph", "name": "Graph" }],
  "activeStudyPlan": "top-interview-150",
  "activeProblemList": "graph",
  "language": "typescript",
  "fileNamePattern": "id",
  "defaultDirectory": "."
}

Requirements

• VS Code or Cursor 1.85+
• Node.js — for TypeScript / JavaScript execution
• Python 3 — optional, for Python solutions
• A C++ toolchain — optional, for C++ solutions
• A JDK (javac + java) — optional, for Java solutions

Development

npm install
npm run compile         # or: npm run watch
npm test                # integration test against LeetCode API
npm run package         # produces a .vsix
npm run install-extension

See CLAUDE.md for a module-by-module architecture tour.

Changelog

See CHANGELOG.md for release notes.

License

MIT

Credits

The Companies sidebar uses problem-frequency / acceptance / topic data sourced from liquidslr/interview-company-wise-problems (snapshot dated 1 June 2025). Many thanks to the upstream maintainers for curating and publishing that dataset.