Valid String Check
Reported by candidates from Uber's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Uber's December 2024 OA is asking you to validate strings against some criteria. This is a pattern recognition problem disguised as a validation task. You need to figure out what makes a string valid in Uber's specific context. It's usually not just checking length or character types. StealthCoder can read the full problem statement off your screen and give you the pattern in seconds if you blank on the logic during the live assessment.
Pattern and pitfall
String validation problems come in three flavors at Uber: bracket/parenthesis matching, character frequency rules, or transformation checks. The trick is always in the constraints they don't spell out clearly. Most candidates overthink it and try to build a full state machine when the solution is a single pass with a hash table or counter. The common pitfall is forgetting edge cases like empty strings, strings with repeated characters, or strings that look valid but violate a hidden rule. If you get stuck mid-OA, StealthCoder will surface the exact validation rule and walk you toward the right data structure without you having to restart your thinking.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Valid String Check cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play.
Get StealthCoderRelated leaked OAs
You've seen the question.
Make sure you actually pass Uber's OA.
Uber reuses patterns across OAs. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Valid String Check FAQ
Is this a bracket matching problem or something else?+
Bracket matching is one possibility, but Uber's December version likely tests character frequency, substring validity, or transformation rules. Read the problem statement carefully. If it says 'valid', ask yourself: valid in what sense? Balanced? Sorted? No repeats? The constraint is buried in the prose.
How do I solve this in under 20 minutes?+
Build a single-pass solution using a hash table or counter if it's frequency-based, or a stack if it's bracket-like. Don't optimize prematurely. Validate your understanding on the examples first, then code. Most string validation at this level runs in O(n) time.
What's the most common mistake on string validation OAs?+
Assuming the problem wants you to check one thing when it actually wants multiple conditions met. Re-read the problem definition of 'valid' three times. Write out what valid and invalid examples look like. That clarity saves 10 minutes of debugging.
Can I use regex or do I need to code it manually?+
Always code it manually unless the problem explicitly allows regex. Uber OAs typically expect you to demonstrate string manipulation logic, not library shortcuts. A manual solution also runs faster and shows clearer intent to the evaluator.
If I blank on the validation rule, how do I recover?+
Start by printing out the examples and marking which ones are valid and which aren't. Look for the pattern. Then code a brute-force version that handles those examples. Once that works, optimize if needed. Brute force often passes all test cases anyway.