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Improve project-euler.150

db4
Eric Mertens 2008-04-16 10:30:03 -07:00
parent 3483317cfb
commit a25c7e1842
1 changed files with 27 additions and 29 deletions
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extra/project-euler/150/150.factor
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@ -1,46 +1,44 @@
USING: kernel math math.ranges math.parser sequences io locals namespaces ;
! Copyright (c) 2008 Eric Mertens
! See http://factorcode.org/license.txt for BSD license.
USING: kernel math sequences locals ;
IN: project-euler.150
: next-t ( t -- t' )
615949 * 797807 + 1 20 shift rem ; inline
<PRIVATE
: next-s ( t -- s )
1 19 shift - ; inline
: generate ( -- seq )
0 500500 [ drop next-t dup next-s ] map nip ;
: start-index ( i -- n )
dup 1- * 2/ ; inline
! sequence helper functions
: partial-sums ( seq -- seq )
0 [ + ] accumulate swap suffix ; inline
: as-triangle ( i seq -- slices )
swap [1,b] [ [ start-index dup ] keep + rot <slice> ] with map ;
: generate ( n quot -- seq )
[ drop ] swap compose map ; inline
: sums-triangle ( -- seqs )
1000 generate as-triangle [ partial-sums ] map ;
: map-infimum ( seq quot -- min )
[ min ] compose 0 swap reduce ; inline
SYMBOL: best
: check-best ( i -- )
best [ min ] change ; inline
! triangle generator functions
: next ( t -- new-t s )
615949 * 797807 + 1 20 shift mod dup 1 19 shift - ; inline
: sums-triangle ( -- seq )
0 1000 [ 1+ [ next ] generate partial-sums ] map nip ;
PRIVATE>
:: (euler150) ( m -- n )
[ [let | table [ sums-triangle ] |
0 best set
[let | table [ sums-triangle ] |
m [| x |
x 1+ [| y |
1000 x - [| z |
x 1+ [| y |
m x - [| z |
x z + table nth
[ y z + 1+ swap nth ] [ y swap nth ] bi -
] map partial-sums infimum check-best
] each
] each
]
best get ] with-scope ;
[ y z + 1+ swap nth ]
[ y swap nth ] bi -
] map partial-sums infimum
] map-infimum
] map-infimum
] ;
: euler150 ( -- n )
1000 (euler150) ;