16 lines
539 B
Common Lisp
16 lines
539 B
Common Lisp
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(load "euler.lisp")
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(defun eratosthenes-helper (expr list-one list-two)
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(if (> (length list-one) 0) (eratosthenes-helper expr (filter (partial expr (first list-one)) (rest list-one)) (filter (partial expr (first list-one)) list-two)) list-two)
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)
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(defun eratosthenes (n)
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(eratosthenes-helper (lambda (x a) (and (eq (mod a x) 0) (/= a x))) (range 2 (sqrt n)) (range 2 n))
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)
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(defun prime-factors (n)
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(select (lambda (a) (eq (mod n a) 0)) (eratosthenes (sqrt n)))
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)
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(defun solution () (first (reverse (prime-factors 600851475143))))
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