Hacker News: rokicki

New comment by rokicki in "Mini Micro Fantasy Computer"

rokicki — Wed, 27 May 2026 15:49:13 +0000

It's so odd that the only nontrivial example code in the paper is completely buggy. The find longest common prefix function of a list of strings fails (try ["a", "bc", "ade"]).

New comment by rokicki in "Ask HN: Hearing aid wearers, what's hot?"

rokicki — Mon, 24 Nov 2025 16:35:42 +0000

For Cochlear brand your kit should include backup coils, and replacement is overnight. If you turn on lights (child mode) the processor lights indicate streaming with blue. I love my cochlear implants even though the integration UI and reliability is not perfect yet.

New comment by rokicki in "S.A.R.C.A.S.M: Slightly Annoying Rubik's Cube Automatic Solving Machine"

rokicki — Sat, 01 Nov 2025 15:33:17 +0000

It should take 105 repetitions:

https://alpha.twizzle.net/explore/?alg=%28U+R%29105

Unless by "same direction" you mean "opposite direction", in which case 63 works:

https://alpha.twizzle.net/explore/?alg=%28U+R%27%2963

Finally: Performant parallel in-place sorting in C++

rokicki — Sun, 06 Apr 2025 17:16:12 +0000

Article URL: https://github.com/GabTux/PPQSort

Comments URL: https://news.ycombinator.com/item?id=43603063

Points: 3

# Comments: 0

New comment by rokicki in "Faster CRDTs (2021)"

rokicki — Wed, 28 Aug 2024 22:01:13 +0000

Nice blog post, but I really wish the author knew how to use apostrophes. (Or the difference between its and it's, if it's not the typographical character he doesn't like.) It's just so jarring to be reading along and be tripped up all the time with grammatical mistakes.

New comment by rokicki in "Why is x & -x equal to the largest power of 2 that divides x?"

rokicki — Tue, 28 May 2024 04:29:05 +0000

This expression is nonzero iff reverse(a) > reverse(b) (where reverse is the bitreversal of an unsigned number).

It (using the address of the nodes as arguments) can serve as a tiebreaker in a Cartesian tree (such as one implementing a first-fit memory allocator) or even to replace the random priority value in a treap (meaning you need neither storage nor computation for the priority node of the treap).

New comment by rokicki in "Why is x & -x equal to the largest power of 2 that divides x?"

rokicki — Sun, 26 May 2024 23:35:02 +0000

There's a nice elegant description of what it does, mathematically, and a significant use in Computer Science.

New comment by rokicki in "Why is x & -x equal to the largest power of 2 that divides x?"

rokicki — Sun, 26 May 2024 18:24:10 +0000

To take this to the next level: what does [(a^b) & (-(a^b)) & a] compute? (Assume unsigned arithmetic.)

And then after that: what use can this be put to?

New comment by rokicki in "Here's a puzzle game. I call it Reverse the List of Integers"

rokicki — Wed, 17 Apr 2024 19:43:01 +0000

To solve a particular position, I just use level-by-level breadth-first search until a level contains two values that are reverses of each other.

To explore the entire state space of possible initial positions, I use a number of tricks; I'll be writing that up pretty soon. I've explored through n=12 already, and expect to finish n=13 and n=14 pretty soon. I'm not sure if I'll be able to do n=15.

And by the way, I've found a position for n=14 that requires 206 moves to solve.

New comment by rokicki in "Here's a puzzle game. I call it Reverse the List of Integers"

rokicki — Mon, 15 Apr 2024 15:57:43 +0000

Finished with a full-state search of 12; worst case is indeed 130. Found a game for n=14 that takes 172 moves: 6 11 8 2 7 10 9 12 4 1 14 3.

New comment by rokicki in "Here's a puzzle game. I call it Reverse the List of Integers"

rokicki — Sun, 14 Apr 2024 15:57:21 +0000

Finished with a full state-space search of 11; worst case is indeed 106 (vs 126 for 10).

New comment by rokicki in "Here's a puzzle game. I call it Reverse the List of Integers"

rokicki — Sun, 14 Apr 2024 04:38:16 +0000

Here are the maximum number of steps required through 10, and likely maximum number of steps required through 12:

6: 14 7: 26 8: 74 9: 86 10: 126 11: 106 (?) (full state space not explored) 12: 130 (?) (full state space not explored)