39 lines
1.2 KiB
Factor
39 lines
1.2 KiB
Factor
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! Copyright (c) 2012 Anonymous
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! See http://factorcode.org/license.txt for BSD license.
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USING: combinators fry kernel lists lists.lazy locals math ;
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IN: rosetta-code.hamming-lazy
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! http://rosettacode.org/wiki/Hamming_numbers#Factor
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! Hamming numbers are numbers of the form
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! H = 2^i * 3^j * 5^k where i, j, k >= 0
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! Hamming numbers are also known as ugly numbers and also
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! 5-smooth numbers (numbers whose prime divisors are less or equal
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! to 5).
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! Generate the sequence of Hamming numbers, in increasing order.
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! In particular:
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! 1. Show the first twenty Hamming numbers.
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! 2. Show the 1691st Hamming number (the last one below 231).
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! 3. Show the one millionth Hamming number (if the language – or
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! a convenient library – supports arbitrary-precision integers).
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:: sort-merge ( xs ys -- result )
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xs car :> x
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ys car :> y
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{
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{ [ x y < ] [ [ x ] [ xs cdr ys sort-merge ] lazy-cons ] }
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{ [ x y > ] [ [ y ] [ ys cdr xs sort-merge ] lazy-cons ] }
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[ [ x ] [ xs cdr ys cdr sort-merge ] lazy-cons ]
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} cond ;
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:: hamming ( -- hamming )
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f :> h!
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[ 1 ] [
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h 2 3 5 [ '[ _ * ] lazy-map ] tri-curry@ tri
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sort-merge sort-merge
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] lazy-cons h! h ;
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