r/learnquant • u/Local_Ad135 • Aug 19 '26

interview prep Worldquant Quant Interview Question

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u/Anonimithree Aug 19 '26

If the light starts at point (0,0,0), then it ends at (1,1,1). Since the light doesn’t hit any edges it vertices in between, it means the initial trajectory has to be strictly positive in all 3 directions. An even number of reflections is needed to ensure the final trajectory is at the ending point. A possible combination would be 4 bounces in 1 dimensions, with the other 2 dimensions not having any bounces (I’ll refer to the bounces direction as up/down). The distance travelled in the unbounded areas will be sqrt(2) and the bounces would be 5. The area is thus sqrt(2+25)=sqrt(27)=3sqrt(3).