alt Hacker News> You have 12 marbles and a balance scale. One of the 12 marbles is inconsistent with the others, meaning it could be heavier or lighter than its peers of normal weight. You are allowed to use the balance scale exactly 3 times to identify which of the 12 marbles is irregular AND determine whether it is heavier or lighter than normal.
I also got this riddle, in 2015. I couldn't solve it. Tbh, I think it's a terrible question. There isn't really a step-by-step problem solving process, but you just need to have a "leap" to realize you can weight the marbles in groups of 3. I also got rejected. It's crazy to get rejected from a one-question riddle like this
> I also got this riddle, in 2015. I couldn't solve it. Tbh, I think it's a terrible question. There isn't really a step-by-step problem solving process, but you just need to have a "leap" to realize you can weight the marbles in groups of 3.
It’s an information theory question similar to the “how far can you drop the egg before it breaks” puzzle. You don’t need a leap of intuition, just remember the right theorems and formulae from college.
I probably would’ve failed the interview. At best I could write an algorithm that empirically arrives at the answer, which may or may not impress the interviewer enough to pass.
Stuff like this is why I dropped out of coding competitions some time in high school. You can always brute force the easy version, then the next tiers drop numbers that cannot be solved unless you know (or can invent) that one weird maths trick.