51 lines
1.2 KiB
Factor
51 lines
1.2 KiB
Factor
! 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.order sequences sequences.private
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locals hints ;
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IN: project-euler.150
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<PRIVATE
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! sequence helper functions
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: partial-sums ( seq -- sums )
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0 [ + ] accumulate swap suffix ; inline
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: (partial-sum-infimum) ( inf sum elt -- inf sum )
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+ [ min ] keep ; inline
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: partial-sum-infimum ( seq -- seq )
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0 0 rot [ (partial-sum-infimum) ] each drop ; inline
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: map-infimum ( seq quot -- min )
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[ min ] compose 0 swap reduce ; inline
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! triangle generator functions
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: next ( t -- new-t s )
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615949 * 797807 + 20 2^ rem dup 19 2^ - ; inline
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: sums-triangle ( -- seq )
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0 1000 [ 1+ [ next ] replicate partial-sums ] map nip ;
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PRIVATE>
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:: (euler150) ( m -- n )
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[let | table [ sums-triangle ] |
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m [| x |
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x 1+ [| y |
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m x - [| z |
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x z + table nth-unsafe
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[ y z + 1+ swap nth-unsafe ]
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[ y swap nth-unsafe ] bi -
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] map partial-sum-infimum
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] map-infimum
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] map-infimum
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] ;
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HINTS: (euler150) fixnum ;
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: euler150 ( -- n )
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1000 (euler150) ;
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