Account for negative loops

src/3n+1/Main.hs

@@ -11,7 +11,11 @@ f' n = f'' 1 n
   where
     f'' :: Integer -> Integer -> Integer
     f'' i n'
-      | n' == 1 = t' i
+      | n' ==   1   = t' 0 + t i
+      | n' ==   0   = t' 0 + t i
+      | n' == (-1 ) = t' 0 + t i
+      | n' == (-5 ) = t' 0 + t i
+      | n' == (-17) = t' 0 + t i
       | even n' = t $ f'' (succ i) (n' `div` 2)
       | odd  n' = t $ f'' (succ i) (3*n' + 1)
       where t   = trace ("i: " ++ show i ++ ", number: " ++ show n')
@@ -24,6 +28,10 @@ f n = s 1 n
     s :: Integer -> Integer -> Integer
     s i n
       | n ==    1  = i
+      | n ==    0  = i
+      | n ==  (-1) = i
+      | n ==  (-5) = i
+      | n == (-17) = i
       | even n = s (succ i) (n `div` 2)
       | odd  n = s (succ i) (3*n + 1)
 
@@ -38,7 +46,11 @@ cc n = cc' [] n
   where
     cc' :: [Integer] -> Integer -> [Integer]
     cc' acc n
-      | n == 1 = 1:acc
+      | n ==    1  = acc <>   [1]
+      | n ==    0  = acc <>   [0]
+      | n ==  (-1) = acc <>  [-1]
+      | n ==  (-5) = acc <>  [-5]
+      | n == (-17) = acc <> [-17]
       | even n = cc' acc' (n `div` 2)
       | odd  n = cc' acc' (3*n + 1)
       where acc' = acc <> [n]