cl-permutation

Permutations and permutation groups in Common Lisp.

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What it is

Permutations and permutation groups in Common Lisp.

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This week on Hacker News

Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 1:49:46 PM UTC.

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Mentions over time

HN mentions by year4 dated mentions

Observed mentions: 2019-05-21 20:15:51 UTC to 2023-08-23 07:00:10 UTC.

Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.

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Period	Start (UTC)	End (exclusive, UTC)	Mentions	Submissions	Comments
2019	2019-01-01 00:00:00 UTC	2020-01-01 00:00:00 UTC	2	1	1
2020	2020-01-01 00:00:00 UTC	2021-01-01 00:00:00 UTC	0	0	0
2021	2021-01-01 00:00:00 UTC	2022-01-01 00:00:00 UTC	0	0	0
2022	2022-01-01 00:00:00 UTC	2023-01-01 00:00:00 UTC	0	0	0
2023	2023-01-01 00:00:00 UTC	2024-01-01 00:00:00 UTC	2	0	2

What Hacker News says

4 sources

reikonomusha·Aug 23, 2023

Here is Lisp code [1] that maps all sorts of combinatorial objects—permutations, combinations, radix-R integers, multi-set arrangements, etc.—perfectly into the smallest set of integers [0, n-1] and back. (In a sense, they are perfect hash functions.) This is used to help efficiently solve combinatorial puzzles. [1] https://github.com/stylewarning/cl-permutation/blob/master/s...

In Permutation iteration and random access

reikonomusha·Jul 9, 2023

There is no need to do iterative deepening as you suggest. The move set L, or more precisely L := C^5 U C^4 U C^3 U C^2 U C^1 U C^0, contains all non-redundant moves sequences of length between 0 and 5. L has 621,649 elements. See e.g. the function that produces this [1]. Solutions thus are found between 0 moves and 20 moves inclusive. If you ask the algorithm to solve a cube with the front face turned, it will immediately output the four words: "", "", "", "F". It will also return every other quadruplet of non-redundant moves that achieve the same state if you keep the solver running, for example: "", "F'", "F", "F" (Here, "non-redundant" means there are no obvious simplifications within each word.) The algorithm is guaranteed to enumerate all non-redundant solutions of bounded length, which includes all optimal solution

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s, in the same worst-case running time of O(N^0.5) and memory complexity of O(N^0.25). The Common Lisp implementation does return on the first match, but that's an implementation detail, not a limitation of the algorithm. Lastly, solutions whose length is short typically show up first, since the words "" * "" correspond to the identity permutation, the lexicographically least permutation, and hence the first permutation found in the search. [1] https://github.com/stylewarning/cl-permutation/blob/master/s...

In Can a Rubik's Cube be brute-forced?

tosh·Jul 22, 2019Submission

cl-permutation: Permutations and Permutation Groups in Common Lisp

1 points · Open discussion

reikonomusha·May 21, 2019

I do computer mathematics. I’m the author of a computational group theory package [2], and my day job is in quantum mechanics and quantum computation, but in that I’m building packages in a software engineering capacity. The algebra gets pretty gnarly. Check out a recent paper, which includes both a math [0] and SW [1] component. Perhaps because of this I’m unusually representative of the intersection between math and software. I hope folks aren’t finding my comments hostile. I have used the Mathematica product before in their GUI and at the command line, and some of my colleagues use it for various calculation tasks. I’ve opted to stick to open source alternatives like Sage, wxMaxima, GAP, and Axiom/Fricas. The engine doesn’t give you a license to Mathematica, so I don’t presume the target audience is the collection of folks who want to

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do differential equations with plots. The article emphasizes lots of software things (languages, integrations, etc.), so actually I do believe they’re targeting software engineers. You should note that I have not criticized their features, but rather restrictions on the use of the product in the first place . Maybe that would be interesting to read, but instead I have commented on the leading question in Wolfram’s article. I have not and will not download their Wolfram engine in its current state though for the reasons I’ve outlined. Do recall that using it means I’m bound to a legal contract, and that’s not one I’m willing to engage with. [0] https://arxiv.org/abs/1904.10541 [1] https://github.com/rigetti/quilc/blob/master/src/compilers/a... [2] https://github.com/stylewarning/cl-permutation

In Free Wolfram Engine for Developers