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Solution to Project Euler problem 52

db4
Aaron Schaefer 2008-02-03 22:11:31 -05:00
parent c64fe3d07b
commit e36bddd91c
2 changed files with 53 additions and 3 deletions
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extra/project-euler/052/052.factor Normal file
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! Copyright (c) 2008 Aaron Schaefer.
! See http://factorcode.org/license.txt for BSD license.
USING: combinators.lib kernel math project-euler.common sequences sorting ;
IN: project-euler.052
! http://projecteuler.net/index.php?section=problems&id=52
! DESCRIPTION
! -----------
! It can be seen that the number, 125874, and its double, 251748, contain
! exactly the same digits, but in a different order.
! Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x,
! contain the same digits.
! SOLUTION
! --------
! Analysis shows the number must be odd, divisible by 3, and larger than 123456
<PRIVATE
: map-nx ( n x -- seq )
[ 1+ * ] with map ; inline
: all-same-digits? ( seq -- ? )
[ number>digits natural-sort ] map all-equal? ;
: candidate? ( n -- ? )
{ [ dup odd? ] [ dup 3 mod zero? ] } && nip ;
: next-all-same ( x n -- n )
dup candidate? [
2dup swap map-nx all-same-digits?
[ nip ] [ 1+ next-all-same ] if
] [
1+ next-all-same
] if ;
PRIVATE>
: euler052 ( -- answer )
6 123456 next-all-same ;
! [ euler052 ] 100 ave-time
! 403 ms run / 7 ms GC ave time - 100 trials
MAIN: euler052

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extra/project-euler/project-euler.factor
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@ -12,9 +12,9 @@ USING: definitions io io.files kernel math math.parser project-euler.ave-time
project-euler.029 project-euler.030 project-euler.031 project-euler.032
project-euler.033 project-euler.034 project-euler.035 project-euler.036
project-euler.037 project-euler.038 project-euler.039 project-euler.040
project-euler.041 project-euler.042 project-euler.048 project-euler.067
project-euler.075 project-euler.134 project-euler.169 project-euler.173
project-euler.175 ;
project-euler.041 project-euler.042 project-euler.048 project-euler.052
project-euler.067 project-euler.075 project-euler.134 project-euler.169
project-euler.173 project-euler.175 ;
IN: project-euler
<PRIVATE