EulerLib, P16, P20, P56, P65, P164: Refactored copies of Haskell digitSum function into new library module.

Author: nayuki

haskell/EulerLib.hs

@@ -0,0 +1,16 @@
+{- 
+ - Shared code for solutions to Project Euler problems
+ - Copyright (c) Project Nayuki. All rights reserved.
+ - 
+ - https://www.nayuki.io/page/project-euler-solutions
+ - https://github.com/nayuki/Project-Euler-solutions
+ -}
+
+module EulerLib
+	(digitSum)
+	where
+
+
+digitSum :: Integral a => a -> a
+digitSum 0 = 0
+digitSum n = (mod n 10) + (digitSum (div n 10))

haskell/p016.hs

@@ -6,10 +6,9 @@
  - https://github.com/nayuki/Project-Euler-solutions
  -}
 
+import EulerLib
+
 
 -- We implement this solution in a straightforward way thanks to Haskell's built-in arbitrary precision Integer type.
 main = putStrLn (show ans)
-ans = digitSum (2^1000 :: Integer)
-
-digitSum 0 = 0
-digitSum n = (mod n 10) + (digitSum (div n 10))
+ans = EulerLib.digitSum (2^1000 :: Integer)

haskell/p020.hs

@@ -6,15 +6,14 @@
  - https://github.com/nayuki/Project-Euler-solutions
  -}
 
+import EulerLib
+
 
 {- 
  - We do a straightforward product thanks to Haskell's built-in arbitrary precision Integer type.
  -}
 
 main = putStrLn (show ans)
-ans = digitSum (factorial 100 :: Integer)
-
-digitSum 0 = 0
-digitSum n = (mod n 10) + (digitSum (div n 10))
+ans = EulerLib.digitSum (factorial 100 :: Integer)
 
 factorial n = product [1..n]

haskell/p056.hs

@@ -6,9 +6,8 @@
  - https://github.com/nayuki/Project-Euler-solutions
  -}
 
+import EulerLib
 
-main = putStrLn (show ans)
-ans = foldl1 max [digitsum (a^b) | a <- [0..99], b <- [0..99]]
 
-digitsum 0 = 0
-digitsum n = (mod n 10) + (digitsum (div n 10))
+main = putStrLn (show ans)
+ans = foldl1 max [EulerLib.digitSum (a^b) | a <- [0..99], b <- [0..99]]

haskell/p065.hs

@@ -6,6 +6,8 @@
  - https://github.com/nayuki/Project-Euler-solutions
  -}
 
+import EulerLib
+
 
 limit = 100
 main = putStrLn (show ans)
@@ -15,12 +17,9 @@ ans = let
 			| otherwise = let (n, d) = func (i+1) end
 			in ((eContFracTerm i) * n + d, n)
 		(numer, _) = func 0 limit
-	in digitSum numer
+	in EulerLib.digitSum numer
 
 eContFracTerm 0 = 2
 eContFracTerm i
 	| mod i 3 == 2 = (div i 3) * 2 + 2
 	| otherwise    = 1
-
-digitSum 0 = 0
-digitSum n = (mod n 10) + (digitSum (div n 10))

haskell/p164.hs

@@ -6,6 +6,8 @@
  - https://github.com/nayuki/Project-Euler-solutions
  -}
 
+import EulerLib
+
 
 base = 10
 digits = 20
@@ -41,9 +43,6 @@ ans = (ways (digits + consecutive) 0) - (ways (digits + consecutive - 1) 0)
 ways :: Int -> Int -> Integer
 ways 0 0 = 1
 ways 0 _ = 0
-ways d p = if (digitSum p) > maxSum then 0
+ways d p = if (EulerLib.digitSum p) > maxSum then 0
 	else sum [waysMemo !! (d - 1) !! ((mod p (base^(consecutive - 1))) * base + i) | i <- [0..9]]
 waysMemo = [[ways d p | p <- [0..]] | d <- [0..]]
-
-digitSum 0 = 0
-digitSum n = (mod n 10) + (digitSum (div n 10))