factor: trim using lists

[factor.git] / extra / project-euler / 215 / 215.factor

diff --git a/extra/project-euler/215/215.factor b/extra/project-euler/215/215.factor
index 056de72e5018a2267b5004e5242aab7abeefca1f..5ae262ff9ad1cfa555d696e60a842c17be2ee865 100644 (file)
--- a/extra/project-euler/215/215.factor
+++ b/extra/project-euler/215/215.factor
@@ -1,21 +1,49 @@
-USING: accessors kernel locals math ;
+! Copyright (c) 2008 Eric Mertens.
+! See http://factorcode.org/license.txt for BSD license.
+USING: accessors kernel math project-euler.common ;
 IN: project-euler.215
 
+! http://projecteuler.net/index.php?section=problems&id=215
+
+! DESCRIPTION
+! -----------
+
+! Consider the problem of building a wall out of 2x1 and 3x1 bricks
+! (horizontal x vertical dimensions) such that, for extra strength, the gaps
+! between horizontally-adjacent bricks never line up in consecutive layers,
+! i.e. never form a "running crack".
+
+! For example, the following 93 wall is not acceptable due to the running crack
+! shown in red:
+
+!     See problem site for image...
+
+! There are eight ways of forming a crack-free 9x3 wall, written W(9,3) = 8.
+
+! Calculate W(32,10).
+
+
+! SOLUTION
+! --------
+
+<PRIVATE
+
 TUPLE: block two three ;
 TUPLE: end { ways integer } ;
 
 C: <block> block
 C: <end> end
-: <failure> 0 <end> ; inline
-: <success> 1 <end> ; inline
+: <failure> ( -- end ) 0 <end> ; inline
+: <success> ( -- end ) 1 <end> ; inline
 
 : failure? ( t -- ? ) ways>> 0 = ; inline
 
-: choice ( t p q -- t t ) [ [ two>> ] [ three>> ] bi ] 2dip bi* ; inline
+: choice ( t p q -- t t )
+    [ [ two>> ] [ three>> ] bi ] 2dip bi* ; inline
 
 GENERIC: merge ( t t -- t )
-GENERIC# block-merge 1 ( t t -- t )
-GENERIC# end-merge 1 ( t t -- t )
+GENERIC#: block-merge 1 ( t t -- t )
+GENERIC#: end-merge 1 ( t t -- t )
 M: block merge block-merge ;
 M: end   merge end-merge ;
 M: block block-merge [ [ two>>   ] bi@ merge ]
@@ -43,14 +71,22 @@ M: end h2 dup failure? [ <failure> <block> ] unless ;
 : next-row ( t -- t ) [ h-1 ] [ h1 ] choice swap <block> ;
 
 : first-row ( n -- t )
-  [ <failure> <success> <failure> ] dip
-  1- [| a b c | b c <block> a b ] times 2drop ;
+    [ <failure> <success> <failure> ] dip
+    1 - [| a b c | b c <block> a b ] times 2drop ;
 
 GENERIC: total ( t -- n )
 M: block total [ total ] dup choice + ;
 M: end   total ways>> ;
 
 : solve ( width height -- ways )
-  [ first-row ] dip 1- [ next-row ] times total ;
+    [ first-row ] dip 1 - [ next-row ] times total ;
+
+PRIVATE>
+
+: euler215 ( -- answer )
+    32 10 solve ;
+
+! [ euler215 ] 100 ave-time
+! 208 ms ave run time - 9.06 SD (100 trials)
 
-: euler215 ( -- ways ) 32 10 solve ;
+SOLUTION: euler215