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rosetta-code.equilibrium-index: simplify.

char-rename
John Benediktsson 2017-02-09 16:04:20 -08:00
parent 3a6eefcc8e
commit 2e73914e85
1 changed files with 8 additions and 11 deletions
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extra/rosetta-code/equilibrium-index/equilibrium-index.factor
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@ -1,11 +1,14 @@
! Copyright (c) 2012 Anonymous
! See http://factorcode.org/license.txt for BSD license.
USING: kernel math math.vectors sequences ;
USING: kernel math math.statistics math.vectors sequences ;
IN: rosetta-code.equilibrium-index
! http://rosettacode.org/wiki/Equilibrium_index
! An equilibrium index of a sequence is an index into the sequence such that the sum of elements at lower indices is equal to the sum of elements at higher indices. For example, in a sequence A:
! An equilibrium index of a sequence is an index into the
! sequence such that the sum of elements at lower indices is
! equal to the sum of elements at higher indices. For example,
! in a sequence A:
! A0 = − 7
! A1 = 1
! A2 = 5
@ -28,12 +31,6 @@ IN: rosetta-code.equilibrium-index
! equilibrium indices (if any). Assume that the sequence may be
! very long.
: accum-left ( seq id quot -- seq )
accumulate nip ; inline
: accum-right ( seq id quot -- seq )
[ <reversed> ] 2dip accum-left <reversed> ; inline
: equilibrium-indices ( seq -- inds )
0 [ + ] [ accum-left ] [ accum-right ] 3bi v=
V{ } swap dup length iota [ [ suffix ] curry [ ] if ] 2each ;
: equilibrium-indices ( seq -- indices )
[ cum-sum0 ] [ <reversed> cum-sum0 <reversed> ] bi
v= t swap indices ;