Solution to Project Euler problem 34

extra/project-euler/034/034.factor

@@ -0,0 +1,47 @@
+! Copyright (c) 2008 Aaron Schaefer.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators.lib kernel math.ranges project-euler.common sequences ;
+IN: project-euler.034
+
+! http://projecteuler.net/index.php?section=problems&id=34
+
+! DESCRIPTION
+! -----------
+
+! 145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145.
+
+! Find the sum of all numbers which are equal to the sum of the factorial of
+! their digits.
+
+! Note: as 1! = 1 and 2! = 2 are not sums they are not included.
+
+
+! SOLUTION
+! --------
+
+! We can reduce the upper bound a little by calculating 7 * 9! = 2540160, and
+! then reducing one of the 9! to 2! (since the 7th digit cannot exceed 2), so we
+! get 2! + 6 * 9! = 2177282 as an upper bound.
+
+! We can then take that one more step, and notice that the largest factorial
+! sum a 7 digit number starting with 21 or 20 is 2! + 1! + 5 * 9! or 1814403.
+! So there can't be any 7 digit solutions starting with 21 or 20, and therefore
+! our numbers must be less that 2000000.
+
+<PRIVATE
+
+: digit-factorial ( n -- n! )
+    { 1 1 2 6 24 120 720 5040 40320 362880 } nth ;
+
+: factorion? ( n -- ? )
+    dup number>digits [ digit-factorial ] sigma = ;
+
+PRIVATE>
+
+: euler034 ( -- answer )
+    3 2000000 [a,b] [ factorion? ] subset sum ;
+
+! [ euler034 ] 10 ave-time
+! 15089 ms run / 725 ms GC ave time - 10 trials
+
+MAIN: euler034

extra/project-euler/common/common.factor

@@ -7,11 +7,11 @@ IN: project-euler.common
 
 ! Problems using each public word
 ! -------------------------------
-! cartesian-product - #4, #27
+! cartesian-product - #4, #27, #29, #32, #33
 ! collect-consecutive - #8, #11
 ! log10 - #25, #134
 ! max-path - #18, #67
-! number>digits - #16, #20, #30
+! number>digits - #16, #20, #30, #34
 ! propagate-all - #18, #67
 ! sum-proper-divisors - #21
 ! tau* - #12

extra/project-euler/project-euler.factor

@@ -1,4 +1,4 @@
-! Copyright (c) 2007 Aaron Schaefer.
+! Copyright (c) 2007, 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: definitions io io.files kernel math.parser sequences vocabs
     vocabs.loader project-euler.ave-time project-euler.common math
@@ -9,7 +9,8 @@ USING: definitions io io.files kernel math.parser sequences vocabs
     project-euler.017 project-euler.018 project-euler.019 project-euler.020
     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.067 project-euler.134
+    project-euler.029 project-euler.030 project-euler.031 project-euler.032
+    project-euler.033 project-euler.034 project-euler.067 project-euler.134
     project-euler.169 project-euler.173 project-euler.175 ;
 IN: project-euler