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feat: add permutations #2

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@olivercalder olivercalder commented Feb 13, 2025

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feat: add first draft of permutation generator
1e91f16 
Signed-off-by: Oliver Calder <oliver@calder.dev>
@olivercalder olivercalder self-assigned this Feb 13, 2025
@olivercalder olivercalder changed the title feat: add first draft of permutation generator feat: add permutations Feb 13, 2025
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feat/permutations: fix bugs and get working permutation generator
a34b840 
Signed-off-by: Oliver Calder <oliver@calder.dev>
@olivercalder
feat/permutations: switch to explicit head and one entry per element
749226b 
In the future, it may be desirable to use a header/footer and get rid of
the `Option<>` wrappers around `prev` and `next`, but the status quo was
a middle ground where the use of `Option<>` made we were checking for
`prev` to be not `None` anyway, so it's easy enough to use an explicit
head, and we were in a painful middle ground.

Additionally, added more doctests for other permutation variants (all
lengths and specified length.

Signed-off-by: Oliver Calder <oliver@calder.dev>
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olivercalder commented Feb 21, 2025

TODO: define custom type to replace Option<usize> which uses 2^64-1 as None, so there's no need to use twice the memory just to store optional integers.

Thanks for the suggestion @paul-rodriguez !

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olivercalder commented Feb 21, 2025

It would also be nice to turn the AvailableList into a trait which supports first() and swap_for_next() methods, and using the current backend as well as a bitset implementation as Paul suggested. We could then benchmark the two implementations with element lists of some huge size (~1 billion?) and permutation lengths of 1, N/2, and N. This would be way too slow at 1 billion, but perhaps we could find a way to benchmark and compare these anyway.

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