Delete empty unit tests files, remove 1- and 1+, reorder IN: lines in a lot of places...

[factor.git] / extra / project-euler / 027 / 027.factor

diff --git a/extra/project-euler/027/027.factor b/extra/project-euler/027/027.factor
index 3ce684549a5f472d7352ff64dea79e4b9b3e750c..f97d8e9e0ddd700dc6b2b339a817d980c0d36908 100644 (file)
--- a/extra/project-euler/027/027.factor
+++ b/extra/project-euler/027/027.factor
@@ -1,6 +1,6 @@
-! Copyright (c) 2007 Aaron Schaefer.
+! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: kernel math math.primes project-euler.common sequences ;
+USING: kernel math math.primes math.ranges project-euler.common sequences ;
 IN: project-euler.027
 
 ! http://projecteuler.net/index.php?section=problems&id=27
@@ -38,26 +38,29 @@ IN: project-euler.027
 
 ! b must be prime since n = 0 must return a prime
 ! a + b + 1 must be prime since n = 1 must return a prime
-! a < b
+! 1 - a + b must be prime as well, hence >= 2. Therefore:
+!    1 - a + b >= 2
+!        b - a >= 1
+!            a < b
 
 <PRIVATE
 
 : source-027 ( -- seq )
-    1000 [ prime? ] subset [ dup [ neg ] map append ] keep
-    cartesian-product [ first2 < ] subset ;
+    1000 [0,b) [ prime? ] filter [ dup [ neg ] map append ] keep
+    cartesian-product [ first2 < ] filter ;
 
 : quadratic ( b a n -- m )
     dup sq -rot * + + ;
 
 : (consecutive-primes) ( b a n -- m )
-    3dup quadratic prime? [ 1+ (consecutive-primes) ] [ 2nip ] if ;
+    3dup quadratic prime? [ 1 + (consecutive-primes) ] [ 2nip ] if ;
 
 : consecutive-primes ( a b -- m )
     swap 0 (consecutive-primes) ;
 
 : max-consecutive ( seq -- elt n )
     dup [ first2 consecutive-primes ] map dup supremum
-    over index [ swap nth ] curry 2apply ;
+    over index [ swap nth ] curry bi@ ;
 
 PRIVATE>
 
@@ -65,8 +68,8 @@ PRIVATE>
     source-027 max-consecutive drop product ;
 
 ! [ euler027 ] 100 ave-time
-! 687 ms run / 23 ms GC ave time - 100 trials
+! 111 ms ave run time - 6.07 SD (100 trials)
 
 ! TODO: generalize max-consecutive/max-product (from #26) into a new word
 
-MAIN: euler027
+SOLUTION: euler027