Factor solution to project Euler problem 17
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! Copyright (c) 2007 Samuel Tardieu.
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! See http://factorcode.org/license.txt for BSD license.
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USING: kernel math namespaces sequences strings ;
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IN: project-euler.017
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! http://projecteuler.net/index.php?section=problems&id=17
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! DESCRIPTION
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! -----------
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! If the numbers 1 to 5 are written out in words: one, two, three, four, five;
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! there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.
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! If all the numbers from 1 to 1000 (one thousand) inclusive were written out
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! in words, how many letters would be used?
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! NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and
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! forty-two) contains 23 letters and 115 (one hundred and fifteen) contains
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! 20 letters.
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! SOLUTION
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! --------
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<PRIVATE
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: units ( n -- )
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{
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"zero" "one" "two" "three" "four" "five" "six" "seven" "eight" "nine"
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"ten" "eleven" "twelve" "thirteen" "fourteen" "fifteen" "sixteen"
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"seventeen" "eighteen" "nineteen"
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} nth % ;
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: tenths ( n -- )
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{
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f f "twenty" "thirty" "fourty" "fifty" "sixty" "seventy" "eighty" "ninety"
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} nth % ;
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DEFER: make-english
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: maybe-add ( n sep -- )
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over 0 = [ 2drop ] [ % make-english ] if ;
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: 0-99 ( n -- )
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dup 20 < [ units ] [ 10 /mod swap tenths "-" maybe-add ] if ;
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: 0-999 ( n -- )
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100 /mod swap
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dup 0 = [ drop 0-99 ] [ units " hundred" % " and " maybe-add ] if ;
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: make-english ( n -- )
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1000 /mod swap
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dup 0 = [ drop 0-999 ] [ 0-999 " thousand" % " and " maybe-add ] if ;
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PRIVATE>
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: >english ( n -- str )
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[ make-english ] "" make ;
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: euler017 ( -- answer )
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1000 [ 1 + >english [ letter? ] subset length ] map sum ;
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! [ euler017 ] 100 ave-time
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! 9 ms run / 0 ms GC ave time - 100 trials
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MAIN: euler017
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