47 lines
1.1 KiB
Factor
47 lines
1.1 KiB
Factor
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USING: kernel math math.ranges math.parser sequences io locals namespaces ;
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IN: project-euler.150
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: next-t ( t -- t' )
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615949 * 797807 + 1 20 shift rem ; inline
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: next-s ( t -- s )
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1 19 shift - ; inline
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: generate ( -- seq )
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0 500500 [ drop next-t dup next-s ] map nip ;
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: start-index ( i -- n )
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dup 1- * 2/ ; inline
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: partial-sums ( seq -- seq )
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0 [ + ] accumulate swap suffix ; inline
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: as-triangle ( i seq -- slices )
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swap [1,b] [ [ start-index dup ] keep + rot <slice> ] with map ;
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: sums-triangle ( -- seqs )
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1000 generate as-triangle [ partial-sums ] map ;
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SYMBOL: best
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: check-best ( i -- )
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best [ min ] change ; inline
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:: (euler150) ( m -- n )
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[ [let | table [ sums-triangle ] |
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0 best set
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m [| x |
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x 1+ [| y |
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1000 x - [| z |
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x z + table nth
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[ y z + 1+ swap nth ] [ y swap nth ] bi -
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] map partial-sums infimum check-best
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] each
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] each
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]
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best get ] with-scope ;
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: euler150 ( -- n )
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1000 (euler150) ;
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