1 ! Copyright (c) 2008 Eric Mertens
2 ! See http://factorcode.org/license.txt for BSD license.
3 USING: kernel math math.order sequences sequences.private
9 ! sequence helper functions
11 : partial-sums ( seq -- sums )
12 0 [ + ] accumulate swap suffix ; inline
14 : (partial-sum-infimum) ( inf sum elt -- inf sum )
15 + [ min ] keep ; inline
17 : partial-sum-infimum ( seq -- seq )
18 0 0 rot [ (partial-sum-infimum) ] each drop ; inline
20 : map-infimum ( seq quot -- min )
21 [ min ] compose 0 swap reduce ; inline
24 ! triangle generator functions
26 : next ( t -- new-t s )
27 615949 * 797807 + 20 2^ rem dup 19 2^ - ; inline
29 : sums-triangle ( -- seq )
30 0 1000 [ 1+ [ next ] replicate partial-sums ] map nip ;
34 :: (euler150) ( m -- n )
35 [let | table [ sums-triangle ] |
39 x z + table nth-unsafe
40 [ y z + 1+ swap nth-unsafe ]
41 [ y swap nth-unsafe ] bi -
42 ] map partial-sum-infimum
47 HINTS: (euler150) fixnum ;