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19 lines
453 B
19 lines
453 B
3 years ago
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module Binomial where
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import Data.MemoTrie
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-- binomial coefficients
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binomial :: Int -> Int -> Integer
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binomial = memo2 b where
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b n k = if k > n
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then 0
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else if n <= 5
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then table !! n !! k
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else binomial (n-1) k + binomial (n-1) (k-1)
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table = [ [1]
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, [1, 1]
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, [1, 2, 1]
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, [1, 3, 3, 1]
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, [1, 4, 6, 4, 1]
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, [1, 5, 10, 10, 5, 1] ]
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