Convert to Base -2
A medium-tier problem at 61% community acceptance, tagged with Math. Reported in interviews at Airbnb and 0 others.
Convert to Base -2 is the kind of problem that sits in the blind spot of most preparation. You think you've done enough on bitwise and number systems, then Airbnb asks you to convert a decimal integer to a negative base and you freeze. The acceptance rate is around 61 percent, which sounds high until you realize most candidates who land here have already drilled the obvious bases. This one punishes the assumption that base conversion is base conversion. If this problem hits your live assessment and the negative base mechanic derails you, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Convert to Base -2"
Convert to Base -2 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 trick: standard base conversion won't work because dividing by a negative number flips the division logic. When you divide by -2, the quotient and remainder have sign relationships that don't match positive-base rules. The pattern is counterintuitive: you can't just take the modulo and divide as usual. Instead, you need to handle the negative base by adjusting remainders to stay non-negative (0 or 1 for base -2), which sometimes forces you to increment the quotient in ways that feel wrong on first read. Most candidates try the positive-base template and watch it fail. The Math topic here is deceptive, because it's really about understanding how division and modulo behave under negation. If you haven't worked through a few negative-base examples by hand, the adjustment logic doesn't click in an interview setting. StealthCoder is the hedge if you blank on why your straightforward approach is producing garbage.
Pattern tags
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Make sure you actually pass it.
Convert to Base -2 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.
Convert to Base -2 interview FAQ
Why doesn't the normal base conversion algorithm work for base -2?+
With positive bases, remainder and quotient follow expected arithmetic rules. With a negative base, division semantics shift: dividing by -2 doesn't produce the same remainder structure as dividing by 2. You must adjust remainders to remain non-negative (0 or 1), which sometimes increments the quotient unexpectedly. This breaks the standard template.
Is this problem still asked at Airbnb?+
Yes. Airbnb appears in the reported companies list for this problem. Airbnb is known for asking problems that sit outside mainstream prep content, and this fits that pattern. If you're interviewing there, treating this as a real possibility is wise.
What's the key insight to solve this without getting stuck?+
Work through a small example by hand first: convert 6 to base -2. Watch how the remainder must stay 0 or 1, and how that forces you to adjust the quotient. Once you see the pattern once, the loop logic becomes mechanical. The insight is that you can't be lazy about the remainder constraint.
How does this relate to other Math topics?+
This is applied number theory and modular arithmetic under non-standard conditions. It touches bitwise thinking (base -2 is binary-adjacent) and modulo behavior, but the real learning is about how axioms break when you introduce negation. It's not a prerequisite for anything else commonly asked.
Is a 61 percent acceptance rate considered high or low?+
It's moderate. For a Medium-difficulty problem, it signals the problem is solvable but not straightforward. You're likely to see candidates who prepped well pass it, but those who relied on generic base-conversion templates will stumble. It's a problem that rewards specific practice.
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