Longest Substring Of All Vowels in Order
A medium-tier problem at 51% community acceptance, tagged with String, Sliding Window. Reported in interviews at Thomson Reuters and 0 others.
You're staring at a string and need to find the longest substring where vowels appear in alphabetical order. Thomson Reuters asked this one, and it's the kind of problem that looks trivial until you realize the string can have consonants, repeats, and skipped vowels all mixed in. The acceptance rate hovers around 50%, which means half the people who see it live either miss the constraint or build something that works on examples but falls apart on edge cases. If this hits your assessment and you blank on the sliding window pattern, StealthCoder runs invisibly during screen share and surfaces a working solution in seconds.
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Longest Substring Of All Vowels in Order 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. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe trick is understanding what 'vowels in order' actually means: you're looking for a substring where vowels appear in the sequence a, e, i, o, u without skipping any vowels. Consonants don't matter and repeats of the same vowel are fine, but the moment a vowel comes out of order, your window resets. The naive approach is to check every substring, which times out. The real solution uses a sliding window or state machine to track which vowel you're currently expecting, extending the window when you see the right vowel or a consonant, and shrinking when you hit a vowel out of order. Common pitfalls: treating this like a normal substring problem without the ordering constraint, or resetting the entire window instead of shrinking strategically. String and Sliding Window together mean you need to think about window validity, not just character presence.
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Longest Substring Of All Vowels in Order 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. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Longest Substring Of All Vowels in Order interview FAQ
Is this actually a medium, or is it easier?+
The acceptance rate of 50% suggests it's genuinely medium. The logic is straightforward once you see it, but the implementation details around window boundaries and the vowel ordering rule trip up people who haven't drilled state machines or sliding windows explicitly.
Do I need to handle uppercase vowels?+
The input doesn't specify, so assume lowercase unless stated. Most online assessments clarify case sensitivity in the problem statement. If you're unsure, code for lowercase first and adjust if the test cases fail.
What if the string has no vowels?+
Return 0 or an empty string depending on the return type. Edge cases like empty input, all consonants, or a single vowel should all return valid results. Build these tests first.
How does this relate to Sliding Window as a topic?+
Sliding Window is core here. You maintain a window of characters where vowels stay in order. When a vowel breaks the sequence, you shrink or reset the window, not rescan from the start. That's what makes it efficient.
Will Thomson Reuters ask follow-ups?+
Thomson Reuters posted this problem, so yes, expect follow-ups. Likely: optimize space, handle Unicode, return the substring itself, or extend to vowels in reverse. Nail the base case first.
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