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Algorithm practice without the editor

Five spare minutes?
Go stretch your brain.

You want to keep your algorithms sharp, but firing up an editor for a coffee-break exercise is a chore — a project, boilerplate, a runtime, and half the effort goes into syntax rather than thinking. So don't write code. Drag the logic together out of blocks, and let Claude tell you whether it actually works.

Start solvingNo sign-up. Works on your phone.
A block diagram solving Two Sum: a loop, a conditional, and a return on each branchNOYESSTARTSETseen = empty mapFOR EACHnum in numsIFseen has target - numSETseen[num] = iRETURN[seen[t-num], i]

Two Sum, as the solver draws it. Arrows are laid out for you; an IF opens a YES and a NO branch that merge back into the flow.

Blocks, not syntax

Ten blocks cover the shape of almost any interview problem. Drop them on the canvas, fill the fields in place, and the diagram wires itself together top to bottom. No semicolons, no off-by-one in a for-loop header, no language to pick — just the reasoning that the exercise was actually about.

  • START
  • END
  • FOR EACH [item] in [collection]
  • IF [condition]
  • SET [variable] = [value]
  • RETURN [value]
  • PUSH [value] to [structure]
  • POP from [structure]
  • INCREMENT [variable]
  • DECREMENT [variable]

Bring your own problems

Five problems ship with it; the rest are yours. Copy a problem straight off LeetCode — the whole page, with the difficulty badge, company tags, acceptance rate and discussion counts still attached — and paste it in. Claude strips the furniture, keeps the constraints that change the algorithm, and turns it into a problem that behaves like any other. Problems you add are visible only to you.

A messy problem page pasted in on the left becomes a clean structured problem on the rightPASTED FROM LEETCODE125. Valid PalindromeInput: s = "race a car"Output: falseCLAUDEYOUR PROBLEMValid PalindromeEXAMPLESInputs = "race a car"OutputfalseInputs = "racecar"Outputtrue

A review, not a green tick

Press Check Solution and Claude reads the diagram as logic. Correct, and it says why it holds. Wrong, and it points at the block that breaks and what to do about it — then leaves a hint for the one thing worth improving next. Solved diagrams are saved so you can come back and see how you thought about it last time.

A review card confirming the logic is correct, with a hint for the next improvement✓ Logic looks correctSaved to your progress.

Progress that follows you

Start solving straight away — nothing to fill in, and your work is kept for this browser. Sign in with GitHub when you want the same problems and solved marks on your laptop and your phone; whatever you already did anonymously comes along with you.

The kettle is still boiling.

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