/extra/project-euler/004/004.factor
http://github.com/abeaumont/factor · Factor · 37 lines · 12 code · 13 blank · 12 comment · 0 complexity · 676c28c9ec7f48079700a75d0836f821 MD5 · raw file
- ! Copyright (c) 2007 Aaron Schaefer, Daniel Ehrenberg.
- ! See http://factorcode.org/license.txt for BSD license.
- USING: hashtables kernel math math.functions math.ranges project-euler.common
- sequences sorting sets ;
- IN: project-euler.004
- ! http://projecteuler.net/index.php?section=problems&id=4
- ! DESCRIPTION
- ! -----------
- ! A palindromic number reads the same both ways. The largest palindrome made
- ! from the product of two 2-digit numbers is 9009 = 91 * 99.
- ! Find the largest palindrome made from the product of two 3-digit numbers.
- ! SOLUTION
- ! --------
- <PRIVATE
- : source-004 ( -- seq )
- 100 999 [a,b] [ 10 divisor? not ] filter ;
- : max-palindrome ( seq -- palindrome )
- natural-sort [ palindrome? ] find-last nip ;
- PRIVATE>
- : euler004 ( -- answer )
- source-004 dup [ * ] cartesian-map combine max-palindrome ;
- ! [ euler004 ] 100 ave-time
- ! 1164 ms ave run time - 39.35 SD (100 trials)
- SOLUTION: euler004