Solution to Project Euler problem 36

extra/project-euler/036/036.factor

@@ -0,0 +1,42 @@
+! Copyright (c) 2008 Aaron Schaefer.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators.lib kernel math.parser math.ranges sequences ;
+IN: project-euler.036
+
+! http://projecteuler.net/index.php?section=problems&id=36
+
+! DESCRIPTION
+! -----------
+
+! The decimal number, 585 = 1001001001 (binary), is palindromic in both bases.
+
+! Find the sum of all numbers, less than one million, which are palindromic in
+! base 10 and base 2.
+
+! (Please note that the palindromic number, in either base, may not include
+! leading zeros.)
+
+
+! SOLUTION
+! --------
+
+! Only check odd numbers since the binary number must begin and end with 1
+
+<PRIVATE
+
+: palindrome? ( str -- ? )
+    dup reverse = ;
+
+: both-bases? ( n -- ? )
+    { [ dup number>string palindrome? ]
+      [ dup >bin palindrome? ] } && nip ;
+
+PRIVATE>
+
+: euler036 ( -- answer )
+    1 1000000 2 <range> [ both-bases? ] subset sum ;
+
+! [ euler036 ] 100 ave-time
+! 3891 ms run / 173 ms GC ave time - 100 trials
+
+MAIN: euler036

extra/project-euler/project-euler.factor

@@ -10,8 +10,9 @@ USING: definitions io io.files kernel math.parser sequences vocabs
     project-euler.021 project-euler.022 project-euler.023 project-euler.024
     project-euler.025 project-euler.026 project-euler.027 project-euler.028
     project-euler.029 project-euler.030 project-euler.031 project-euler.032
-    project-euler.033 project-euler.034 project-euler.035 project-euler.067
-    project-euler.134 project-euler.169 project-euler.173 project-euler.175 ;
+    project-euler.033 project-euler.034 project-euler.035 project-euler.036
+    project-euler.067 project-euler.134 project-euler.169 project-euler.173
+    project-euler.175 ;
 IN: project-euler
 
 <PRIVATE