Partial progress for problem 74

74.hs

@@ -0,0 +1,41 @@
+import Data.Char (digitToInt)
+
+digitFactorial :: Integer -> Integer
+digitFactorial n = case n of 
+    0 -> 1
+    1 -> 1
+    2 -> 2
+    3 -> 6
+    4 -> 24
+    5 -> 120
+    6 -> 720
+    7 -> 5040
+    8 -> 40320
+    9 -> 362880
+
+sizeOfLoop :: Integer -> Integer
+sizeOfLoop n 
+    | n == 169 || n == 363601 || n == 1454 = 3
+    | n == 871 || n == 45361 = 2
+    | n == 872 || n == 45362 = 2
+    | n == 145 || n == 1 || n == 2 = 1
+    | otherwise = 0
+
+sumOfFactorialOfDigits :: Integer -> Integer
+sumOfFactorialOfDigits n = sum $ map (digitFactorial . fromIntegral . digitToInt) $ show n
+
+getChainLength :: Integer -> Integer
+getChainLength n = getChainLengthRec n 1
+
+getChainLengthRec :: Integer -> Integer -> Integer
+getChainLengthRec n length = 
+    let next = sumOfFactorialOfDigits n
+        nextLength = sizeOfLoop next
+    in if nextLength == 0 
+       then getChainLengthRec next (length + 1)
+       else length + nextLength
+       
+numOfLoops :: Integer -> Integer -> Integer
+numOfLoops bound length = foldr (\n num -> num + if getChainLength n == length then 1 else 0) 0 [3..bound]
+
+main = print $ numOfLoops 1000000 60