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Practice coding interviews out loud with real-time voice coaching. Your code actually runs.
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Valid Parentheses
This is a stack/invariant problem: once your stack represents the right thing, the rest is routine. It's a great warm-up that builds stack invariants without a ton of moving parts. Keep the stack invariant explicit; if it breaks, everything downstream breaks too.
Meet Allison & Tim
Your AI coaches
Practice coding interviews out loud with real-time voice coaching. Your code actually runs.
Desktop required to run this problem
StrongYes runs real code + tests in a desktop editor. Mobile is view-only for now, so you can’t start this here. Sorry about that — email yourself a link and pick it up on your computer.
Start Part 1 to unlock your next challenge
Desktop required
Sorry — mobile can’t run the editor + tests yet. Email yourself a link to continue on desktop.