factor: trim using lists

[factor.git] / extra / project-euler / 175 / 175.factor

diff --git a/extra/project-euler/175/175.factor b/extra/project-euler/175/175.factor
index db1760c0179a3ab47b99b4f2a1e80072b54b751a..9f47c343d5c46924f7b3de9f5cc5849def55efea 100644 (file)
--- a/extra/project-euler/175/175.factor
+++ b/extra/project-euler/175/175.factor
@@ -1,6 +1,7 @@
 ! Copyright (c) 2007 Samuel Tardieu.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: combinators kernel math math.parser math.ranges sequences vectors ;
+USING: combinators kernel math math.parser project-euler.common
+sequences ;
 IN: project-euler.175
 
 ! http://projecteuler.net/index.php?section=problems&id=175
@@ -8,47 +9,51 @@ IN: project-euler.175
 ! DESCRIPTION
 ! -----------
 
-! Define f(0)=1 and f(n) to be the number of ways to write n as a sum of
+! Define f(0) = 1 and f(n) to be the number of ways to write n as a sum of
 ! powers of 2 where no power occurs more than twice.
 
-! For example, f(10)=5 since there are five different ways to express
+! For example, f(10) = 5 since there are five different ways to express
 ! 10: 10 = 8+2 = 8+1+1 = 4+4+2 = 4+2+2+1+1 = 4+4+1+1
 
-! It can be shown that for every fraction p/q (p0, q0) there exists at
-! least one integer n such that f(n)/f(n-1)=p/q.
+! It can be shown that for every fraction p/q (p0, q0) there exists at least
+! one integer n such that f(n) / f(n-1) = p/q.
 
-! For instance, the smallest n for which f(n)/f(n-1)=13/17 is 241.  The
-! binary expansion of 241 is 11110001.  Reading this binary number from
-! the most significant bit to the least significant bit there are 4
-! one's, 3 zeroes and 1 one. We shall call the string 4,3,1 the
-! Shortened Binary Expansion of 241.
+! For instance, the smallest n for which f(n) / f(n-1) = 13/17 is 241. The
+! binary expansion of 241 is 11110001. Reading this binary number from the most
+! significant bit to the least significant bit there are 4 one's, 3 zeroes and
+! 1 one. We shall call the string 4,3,1 the Shortened Binary Expansion of 241.
 
 ! Find the Shortened Binary Expansion of the smallest n for which
-! f(n)/f(n-1)=123456789/987654321.
+! f(n) / f(n-1) = 123456789/987654321.
 
 ! Give your answer as comma separated integers, without any whitespaces.
 
+
 ! SOLUTION
 ! --------
 
+<PRIVATE
+
 : add-bits ( vec n b -- )
-  over zero? [
-    3drop
-  ] [
-    pick length 1 bitand = [ over pop + ] when swap push
-  ] if ;
+    over zero? [
+        3drop
+    ] [
+        pick length 1 bitand = [ over pop + ] when swap push
+    ] if ;
 
 : compute ( vec ratio -- )
-  {
-    { [ dup integer? ] [ 1- 0 add-bits ] }
-    { [ dup 1 < ] [ 1 over - / dupd compute 1 1 add-bits ] }
-    { [ t ] [ [ 1 mod compute ] 2keep >integer 0 add-bits ] }
-  } cond ;
+    {
+        { [ dup integer? ] [ 1 - 0 add-bits ] }
+        { [ dup 1 < ] [ 1 over - / dupd compute 1 1 add-bits ] }
+        [ [ 1 mod compute ] 2keep >integer 0 add-bits ]
+    } cond ;
+
+PRIVATE>
 
 : euler175 ( -- result )
-  V{ 1 } clone dup 123456789/987654321 compute [ number>string ] map "," join ;
+    V{ 1 } clone dup 123456789/987654321 compute [ number>string ] map "," join ;
 
 ! [ euler175 ] 100 ave-time
-! 0 ms run / 0 ms GC ave time - 100 trials
+! 0 ms ave run time - 0.31 SD (100 trials)
 
-MAIN: euler175
+SOLUTION: euler175