25 lines
519 B
Factor
25 lines
519 B
Factor
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! Copyright (c) 2008 Eric Mertens
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! See http://factorcode.org/license.txt for BSD license.
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USING: kernel math math.functions sequences sequences.lib ;
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IN: project-euler.148
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<PRIVATE
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: sum-1toN ( n -- sum )
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dup 1+ * 2/ ; inline
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: >base7 ( x -- y )
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[ dup 0 > ] [ 7 /mod ] [ ] unfold nip ;
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: (use-digit) ( prev x index -- next )
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[ [ 1+ * ] [ sum-1toN 7 sum-1toN ] bi ] dip ^ * + ;
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PRIVATE>
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: (euler148) ( x -- y )
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>base7 0 [ (use-digit) ] reduce-index ;
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: euler148 ( -- y )
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10 9 ^ (euler148) ;
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