Solution to Project Euler problem 30

extra/project-euler/030/030.factor

@@ -0,0 +1,46 @@
+! Copyright (c) 2007 Aaron Schaefer.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators.lib kernel math math.functions project-euler.common sequences ;
+IN: project-euler.030
+
+! http://projecteuler.net/index.php?section=problems&id=30
+
+! DESCRIPTION
+! -----------
+
+! Surprisingly there are only three numbers that can be written as the sum of
+! fourth powers of their digits:
+
+!     1634 = 1^4 + 6^4 + 3^4 + 4^4
+!     8208 = 8^4 + 2^4 + 0^4 + 8^4
+!     9474 = 9^4 + 4^4 + 7^4 + 4^4
+
+!     As 1 = 1^4 is not a sum it is not included.
+
+! The sum of these numbers is 1634 + 8208 + 9474 = 19316.
+
+! Find the sum of all the numbers that can be written as the sum of fifth
+! powers of their digits.
+
+
+! SOLUTION
+! --------
+
+! if n is the number of digits
+! n * 9^5 = 10^n  when n ≈ 5.513
+! 10^5.513 ≈ 325537
+
+<PRIVATE
+
+: sum-fifth-powers ( n -- sum )
+    number>digits [ 5 ^ ] sigma ;
+
+PRIVATE>
+
+: euler030 ( -- answer )
+    325537 [ dup sum-fifth-powers = ] subset sum 1- ;
+
+! [ euler030 ] 100 ave-time
+! 2537 ms run / 125 ms GC ave time - 100 trials
+
+MAIN: euler030

extra/project-euler/common/common.factor

@@ -11,7 +11,7 @@ IN: project-euler.common
 ! collect-consecutive - #8, #11
 ! log10 - #25, #134
 ! max-path - #18, #67
-! number>digits - #16, #20
+! number>digits - #16, #20, #30
 ! propagate-all - #18, #67
 ! sum-proper-divisors - #21
 ! tau* - #12

extra/project-euler/project-euler.factor

@@ -9,8 +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.067 project-euler.134 project-euler.169
+    project-euler.029 project-euler.030 project-euler.067 project-euler.134
-    project-euler.173 project-euler.175 ;
+    project-euler.169 project-euler.173 project-euler.175 ;
 IN: project-euler
 
 <PRIVATE