/extra/project-euler/002/002.factor
http://github.com/abeaumont/factor · Factor · 80 lines · 32 code · 28 blank · 20 comment · 5 complexity · 7d901ca8bf11c10c62887454d505e4e3 MD5 · raw file
- ! Copyright (c) 2007, 2008 Aaron Schaefer, Alexander Solovyov, Vishal Talwar.
- ! See http://factorcode.org/license.txt for BSD license.
- USING: kernel math sequences project-euler.common ;
- IN: project-euler.002
- ! http://projecteuler.net/index.php?section=problems&id=2
- ! DESCRIPTION
- ! -----------
- ! Each new term in the Fibonacci sequence is generated by adding the previous
- ! two terms. By starting with 1 and 2, the first 10 terms will be:
- ! 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
- ! Find the sum of all the even-valued terms in the sequence which do not exceed
- ! four million.
- ! SOLUTION
- ! --------
- <PRIVATE
- : (fib-upto) ( seq n limit -- seq )
- 2dup <= [ [ over push dup 2 tail* sum ] dip (fib-upto) ] [ 2drop ] if ;
- PRIVATE>
- : fib-upto ( n -- seq )
- V{ 0 } clone 1 rot (fib-upto) ;
- : euler002 ( -- answer )
- 4,000,000 fib-upto [ even? ] filter sum ;
- ! [ euler002 ] 100 ave-time
- ! 0 ms ave run time - 0.22 SD (100 trials)
- ! ALTERNATE SOLUTIONS
- ! -------------------
- : fib-upto* ( n -- seq )
- 0 1 [ pick over >= ] [ [ nip ] 2keep + dup ] produce [ 3drop ] dip
- but-last-slice { 0 1 } prepend ;
- : euler002a ( -- answer )
- 4,000,000 fib-upto* [ even? ] filter sum ;
- ! [ euler002a ] 100 ave-time
- ! 0 ms ave run time - 0.2 SD (100 trials)
- <PRIVATE
- : next-fibs ( x y -- y x+y )
- [ nip ] [ + ] 2bi ;
- : ?retotal ( total fib- fib+ -- retotal fib- fib+ )
- dup even? [ [ nip + ] 2keep ] when ;
- : (sum-even-fibs-below) ( partial fib- fib+ max -- total )
- 2dup > [
- 3drop
- ] [
- [ ?retotal next-fibs ] dip (sum-even-fibs-below)
- ] if ;
- PRIVATE>
- : sum-even-fibs-below ( max -- sum )
- [ 0 0 1 ] dip (sum-even-fibs-below) ;
- : euler002b ( -- answer )
- 4000000 sum-even-fibs-below ;
- ! [ euler002b ] 100 ave-time
- ! 0 ms ave run time - 0.0 SD (100 trials)
- SOLUTION: euler002b