Minimum Remove to Make Valid Parentheses
A medium-tier problem at 71% community acceptance, tagged with String, Stack. Reported in interviews at Meta and 6 others.
You're at 70% acceptance rate, which sounds high until you realize this is the problem that trips up candidates who skip the string-parsing fundamentals. Meta, Google, Netflix, and Snap all ask it. The trap is thinking you need to be clever. You don't. The problem is straightforward: remove characters to leave only valid parentheses. But speed matters in a live assessment, and the obvious two-pass approach can feel clunky under pressure. If you blank on the indexing logic or the stack trick during your OA, StealthCoder solves it invisibly in seconds.
Companies that ask "Minimum Remove to Make Valid Parentheses"
Minimum Remove to Make Valid Parentheses is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage.
Get StealthCoderThe core pattern is stack-based validation with deletion. You either track invalid indices and rebuild the string, or you use a stack to match pairs and skip unmatched ones. Most candidates default to a stack approach because it maps cleanly to the problem: push opening parens, pop on closing parens, and anything left unmatched gets marked for removal. The real gotcha is the string reconstruction step. After you've identified which characters to keep, you still have to build the output string correctly, and off-by-one errors on index ranges are common under time pressure. The String and Stack topics are both mandatory here. If you've drilled balanced-parentheses problems, you'll recognize the shape immediately. If not, the logic is learnable in five minutes, but you won't have five minutes in the assessment. StealthCoder is the hedge for when the pattern doesn't click fast enough.
Pattern tags
You know the problem.
Make sure you actually pass it.
Minimum Remove to Make Valid Parentheses recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Remove to Make Valid Parentheses interview FAQ
Is this problem actually asked at Meta and Google, or just reported?+
It's in the reported-ask lists for both, along with Netflix, Snap, Bloomberg, GE Digital, and Tencent. That's seven companies across different industries, so it's not a one-off. Expect it to stay in rotation.
Can I solve this without a stack?+
Yes. You can make two passes: first mark all invalid indices, then rebuild the string skipping them. Both approaches are O(n) time and space. The stack way feels more elegant if you're comfortable with the data structure.
What's the most common mistake on this problem?+
Forgetting to handle the string reconstruction after marking invalid indices. Or using a stack but not converting it back to a string properly. Index arithmetic breaks under pressure. That's where most candidates lose time.
How does this relate to other stack problems I should know?+
It's a variant of valid-parentheses checking, but with the twist that you must output a cleaned string. If you've solved the basic valid-parentheses problem, you're halfway there. The removal step is the new piece.
With 70% acceptance, is this a warning that something's tricky?+
Not really. 70% means most people pass, but not everyone finishes clean on the first try. Usually it's the string reconstruction that bleeds time. It's a medium for good reason: easy to understand, easy to mess up in implementation.
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