2008-02-02 18:53:32 -05:00
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! Copyright (c) 2008 Aaron Schaefer.
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! See http://factorcode.org/license.txt for BSD license.
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USING: kernel math math.parser sequences strings ;
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IN: project-euler.040
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! http://projecteuler.net/index.php?section=problems&id=40
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! DESCRIPTION
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! -----------
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! An irrational decimal fraction is created by concatenating the positive
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! integers:
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! 0.123456789101112131415161718192021...
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! It can be seen that the 12th digit of the fractional part is 1.
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! If dn represents the nth digit of the fractional part, find the value of the
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! following expression.
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! d1 × d10 × d100 × d1000 × d10000 × d100000 × d1000000
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! SOLUTION
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! --------
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<PRIVATE
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: (concat-upto) ( n limit str -- str )
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2dup length > [
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pick number>string over push-all rot 1+ -rot (concat-upto)
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] [
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2nip
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] if ;
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: concat-upto ( n -- str )
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SBUF" " clone 1 -rot (concat-upto) ;
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: nth-integer ( n str -- m )
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2008-02-06 22:15:47 -05:00
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[ 1- ] dip nth 1string string>number ;
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2008-02-02 18:53:32 -05:00
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PRIVATE>
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: euler040 ( -- answer )
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1000000 concat-upto { 1 10 100 1000 10000 100000 1000000 }
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[ swap nth-integer ] with map product ;
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! [ euler040 ] 100 ave-time
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! 1002 ms run / 43 ms GC ave time - 100 trials
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MAIN: euler040
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