When algorithms click

A tutor for every algorithm pattern.

Every lesson shows the algorithm in motion, names the bug behind your failing case, and answers your follow-up questions in plain English. The complete SWE interview path, taught all the way through.

The tutor

Inside every lesson

Four building blocks you won't find in a list of problems or a wall of text.

Two pointers· Two Sum IItarget = 18lohi257111317012345a[lo] + a[hi] = 19> target → hi--

Algorithm walkthrough

Watch the pattern in motion at your own pace. Two pointers converging, a hash map filling cell by cell, a tree expanding wave by wave — every cursor labelled, every step explained.

Hint stack· three levels, you pick how farLEVEL 3The exact gap in your code7 ptLEVEL 2The trick behind the pattern3 ptLEVEL 1A nudge toward the right idea1 pt

Hints that build intuition

Stuck? A nudge toward the right idea. Stuck again? The trick behind the pattern. Still stuck? The exact gap in your code. Each level costs mastery points so you spend only what you need.

Submission failed· case [3,3], target 61whilelo <= hi:2 s = a[lo] + a[hi]3 if s == target: return4 elif s < target: lo += 15 else: hi -= 1THE BUGOff-by-oneon the upperboundlo == hi sums one cell twice

Feedback that names the bug

When your code fails, you see the actual mistake behind it: off-by-one on the upper bound, missing edge case on empty input, mutating while iterating. Fix the thinking and the symptom resolves with it.

Ask the tutor· grounded in your code2 pt / ansYOUWhy is it safe to drop hiwhen the sum exceeds target?TUTORSorted means every cell right of hiis bigger. None can pair with a[lo]to hit target — hi-- is lossless.

Ask the tutor anything

Type a question in plain English and get an answer grounded in this problem and the code you wrote. Each answer costs mastery points, the same as a hint, so it stays a learning aid rather than an autocomplete.

When something breaks

The tutor explains

Submit a buggy solution and the tutor reads the same result you do. It walks the visual to the moment your reasoning slipped and writes one or two sentences of what actually went wrong. Ask a follow-up about the trick, the edge case, or why your fix moved the failure elsewhere, and the answer stays inside the world of this problem and your code.

  1. Case 4 / 12· failedINPUTnums = [2, 7, 11, 15], target = 9YOUR OUTPUT[0, 0]EXPECTED[0, 1]
    01

    Submission lands on a failing case

    The tutor sees the gap between what your code returned and what the case expected.

  2. Diagnosis· step 5 / 8SCROLLED TO WHERE IT SHOWS UPlo = hi711IN PLAIN ENGLISHOff-by-one — lo passed hi, summed one cell twice.
    02

    The bug gets named in plain English

    A short message points at the wrong comparison, the missing parity term, the index that fell off by one. The visual scrolls to the step where it shows up.

  3. Follow-ups· Two Sum IIANCHOREDwhat's the loop invariant here?TUTOREvery answer pair sits inside [lo, hi].Shrinking can't skip a valid pair —sorted order rules out the dropped side.why does that fail on duplicates?COST−4 pt2 questions · same as 2 hints
    03

    Follow-ups stay in this lesson

    Ask why your fix loops forever, why the trick works, or what changes for the empty input. Each answer is keyed to your code, costs mastery like a hint, and keeps the path forward yours.

The path

Adapts to where you stand

Algotrek tracks what you've practiced and what you're ready for next. The path adapts as you go, and stale concepts come back for review.

  • Only shows concepts you have the foundations for

  • Mastery fades like memory does — stale concepts come back for review so they stick

  • MASTERY−2 pt · hint

    Hints debit your mastery score, so you only take what you need

  • { }CODETUTORQUIZ+ mastery

    Quizzes carry as much mastery as writing code or talking to the tutor — and they surface the sharpest questions to ask next

Languages

Write in the language you'll interview in.

JavaScriptTypeScriptPythonC++JavaGoRustDart
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Algotrek

A tutor for every algorithm pattern. Visual walkthroughs, smart hints, feedback that names your mistake.

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The path

Adaptive. Teaching-first. Built for engineers who'd rather understand than grind.

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