46 lines
1.1 KiB
Factor
46 lines
1.1 KiB
Factor
! Copyright (c) 2007 Aaron Schaefer.
|
|
! See http://factorcode.org/license.txt for BSD license.
|
|
USING: kernel math project-euler.common ;
|
|
IN: project-euler.012
|
|
|
|
! http://projecteuler.net/index.php?section=problems&id=12
|
|
|
|
! DESCRIPTION
|
|
! -----------
|
|
|
|
! The sequence of triangle numbers is generated by adding the natural numbers.
|
|
! So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first
|
|
! ten terms would be:
|
|
|
|
! 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...
|
|
|
|
! Let us list the factors of the first seven triangle numbers:
|
|
|
|
! 1: 1
|
|
! 3: 1,3
|
|
! 6: 1,2,3,6
|
|
! 10: 1,2,5,10
|
|
! 15: 1,3,5,15
|
|
! 21: 1,3,7,21
|
|
! 28: 1,2,4,7,14,28
|
|
|
|
! We can see that the 7th triangle number, 28, is the first triangle number to
|
|
! have over five divisors.
|
|
|
|
! Which is the first triangle number to have over five-hundred divisors?
|
|
|
|
|
|
! SOLUTION
|
|
! --------
|
|
|
|
: nth-triangle ( n -- n )
|
|
dup 1+ * 2 / ;
|
|
|
|
: euler012 ( -- answer )
|
|
8 [ dup nth-triangle tau* 500 < ] [ 1+ ] [ ] while nth-triangle ;
|
|
|
|
! [ euler012 ] 10 ave-time
|
|
! 5413 ms run / 1 ms GC ave time - 10 trials
|
|
|
|
MAIN: euler012
|