From 78d4ca5aeaf1bfc52eb4c4999755a9e0bf1d4a22 Mon Sep 17 00:00:00 2001
From: Bill Ewanick <bill@ewanick.com>
Date: Fri, 20 Oct 2023 02:23:50 -0400
Subject: [PATCH] Account for negative loops

---
 src/3n+1/Main.hs | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/3n+1/Main.hs b/src/3n+1/Main.hs
index e42bbb5..b516e74 100755
--- a/src/3n+1/Main.hs
+++ b/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')
@@ -23,7 +27,11 @@ f n = s 1 n
   where
     s :: Integer -> Integer -> Integer
     s i n
-      | n == 1 = i
+      | 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]