Hexspeak
A easy-tier problem at 58% community acceptance, tagged with Math, String. Reported in interviews at Virtu Financial and 0 others.
Hexspeak is an easy problem that asks whether a number can be represented using only hexadecimal digits that look like letters: A, B, C, D, E, F. At first it sounds trivial, but the gotcha is that 0, 1, and 8 look like digits even in hex notation, so they're forbidden. Virtu Financial asks this. The acceptance rate is solid at 58%, which means roughly four out of ten candidates miss the constraint or botch the validation. It's the kind of problem where you either nail it in 90 seconds or you second-guess yourself into a bug.
Companies that ask "Hexspeak"
Hexspeak 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 Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe trap is misreading what 'hexspeak' means. You need to validate that every character in the input string is one of A, B, C, D, E, F only. Numbers like 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 are not allowed, even though 0-9 are technically valid hex digits. Most people's first instinct is to check if the string is a valid hex number, which is wrong. A one-liner regex or a simple character set check solves it. The real work is reading the problem statement carefully and not confusing 'valid hex' with 'valid hexspeak'. If this hits your live OA and you blank on the exact rules, StealthCoder surfaces a working solution invisible to the proctor.
Pattern tags
You know the problem.
Make sure you actually pass it.
Hexspeak recycles across companies for a reason. It's easy-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 Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Hexspeak interview FAQ
Why is the acceptance rate only 58% if this is easy?+
Most failures come from misreading the constraint. Candidates assume 'hex digits' means all 0-9 and A-F, then submit a hex validator that accepts numbers. The problem explicitly forbids 0, 1, and 8. Careful reading on your first pass saves a resubmission.
What's the trick to Hexspeak?+
There isn't one. It's pure constraint validation. Read the problem statement word-for-word, identify exactly which characters are allowed, then check each character against that set. A simple loop or regex does the job in under a minute.
How does Hexspeak relate to String and Math topics?+
String because you're iterating and validating characters. Math because hexadecimal notation is mathematical notation. Neither requires advanced algorithms. Both topics are surface-level here, which is why the difficulty is easy.
Do I need to convert to an integer or check string representation?+
Work with the string directly. You don't need to convert or calculate anything. Just iterate through each character and verify it's in the allowed set. Conversion adds unnecessary overhead and risk of mishandling the rules.
Will Virtu Financial ask this in a real interview?+
Virtu Financial is reported to have asked this problem. It's a screening-style question, not a system-design problem. Expect it as a warm-up or a second or third question in a timed online assessment, not a conversation opener.
Want the actual problem statement? View "Hexspeak" on LeetCode →