factor: trim using lists

[factor.git] / extra / project-euler / 044 / 044.factor

diff --git a/extra/project-euler/044/044.factor b/extra/project-euler/044/044.factor
index 0af3a3167ef7c647dda0237d90bee2da62cdbd27..747e058eb53311c11c1cc04984bf18564d513c72 100644 (file)
--- a/extra/project-euler/044/044.factor
+++ b/extra/project-euler/044/044.factor
@@ -1,6 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: kernel math math.functions math.ranges project-euler.common sequences ;
+USING: kernel math ranges math.order project-euler.common
+sequences layouts ;
 IN: project-euler.044
 
 ! http://projecteuler.net/index.php?section=problems&id=44
@@ -28,20 +29,26 @@ IN: project-euler.044
 <PRIVATE
 
 : nth-pentagonal ( n -- seq )
-    dup 3 * 1- * 2 / ;
+    dup 3 * 1 - * 2 /i ; inline
 
 : sum-and-diff? ( m n -- ? )
-    [ + ] [ - ] 2bi [ pentagonal? ] bi@ and ;
+    [ + ] [ - ] 2bi [ pentagonal? ] both? ; inline
+
+: euler044-step ( min m n -- min' )
+    [ nth-pentagonal ] bi@
+    2dup sum-and-diff? [ - abs min ] [ 2drop ] if ; inline
 
 PRIVATE>
 
 : euler044 ( -- answer )
-    2500 [1,b] [ nth-pentagonal ] map dup cartesian-product
-    [ first2 sum-and-diff? ] filter [ first2 - abs ] map infimum ;
+    most-positive-fixnum
+    2500 [1..b] [
+        dup [1..b] [
+            euler044-step
+        ] with each
+    ] each ;
 
 ! [ euler044 ] 10 ave-time
-! 5727 ms ave run time - 1102.38 SD (10 trials)
-
-! TODO: this solution is ugly and not very efficient...find a better algorithm
+! 289 ms ave run time - 0.27 SD (10 trials)
 
-MAIN: euler044
+SOLUTION: euler044