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Improve performance of derangement/subfactorial with iterative implementation #146

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Improve performance of derangement/subfactorial with iterative implementation #146

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Commits on Dec 10, 2023

  1. Improve performance of derangement/subfactorial with iterative im… 

    …plementation

Use the recursive formula
  !n = (n-1) * (!(n-1) + !(n-2))
presented here: https://en.wikipedia.org/wiki/Derangement#Counting_derangements
    @FedericoStra
    FedericoStra committed Dec 10, 2023
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Commits on Dec 13, 2023

  1. Improve performance of derangement/subfactorial with simpler recu… 

    …rsive formula and inplace computations

Use the simpler formula

!n = n * !(n-1) + (-1)^n

and use inplace operations on `BigInt`s to avoid allocations.
    @FedericoStra
    FedericoStra committed Dec 13, 2023
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