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Google's “Director of Engineering” Hiring Test

(www.gwan.com)
1764 points fatihky | 1 comments | 13 Oct 16 15:15 UTC | HN request time: 0.222s | source
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greyman ◴[13 Oct 16 17:53 UTC] No.12702663[source]▶
I once coded chess playing algorithm for fun, and can confirm that the recruiter was correct on #9: you count bits by using a lookup table and then sum the results. It's the quickest way. But I am not sure if this is possible to figure out immediately without such experience...
replies(3): >>12702773 #>>12703527 #>>12708596 #
1. Const-me ◴[14 Oct 16 15:13 UTC] No.12708596[source]▶
I recently tested different approaches. I’ve been working on some code that downsamples large set of 1 bit voxels to get shades of gray on the edges. For that, I had to counts gigabytes of those bits as fast as possible.

Advanced manually-vectorized SIMD code worked several times faster that lookup, esp. on the hardware that supports SSSE3 or XOP instructions.

And even when the hardware doesn’t have SSE4, doesn’t have SSSE3, doesn’t have XOP — SSE2-only backup plan is still faster than lookup tables. Here’s the code: http://stackoverflow.com/a/17355341/126995