From bc28995115a02e665cb8d9cc8228f21ace5319f3 Mon Sep 17 00:00:00 2001
From: Bill Ewanick <bill@ewanick.com>
Date: Wed, 27 Sep 2023 16:51:16 -0400
Subject: [PATCH] Add performance improvement

---
 src/projectEuler/question14.hs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/projectEuler/question14.hs b/src/projectEuler/question14.hs
index 34cf393..a4128ed 100644
--- a/src/projectEuler/question14.hs
+++ b/src/projectEuler/question14.hs
@@ -16,14 +16,14 @@ NOTE: Once the chain starts the terms are allowed to go above one million.
 -}
 module Main where
 
-import           Data.List (sortOn)
+import           Data.List (genericLength, sortOn)
 import           Data.Ord  (Down (Down))
 
 main :: IO ()
 main = print ans
 
 ans :: Integer
-ans = head $ head $ sortOn (Down . length) $ map collatzChainStartingAt [1..limit]
+ans = fst $ head $ sortOn (Down . snd) $ map collatzChainStartingAt [1..limit]
 
 nextCollatz :: Integer -> Integer
 nextCollatz n
@@ -31,8 +31,9 @@ nextCollatz n
   | even n = n `div` 2
   | odd  n = 3*n + 1
 
-collatzChainStartingAt :: Integer -> [Integer]
-collatzChainStartingAt n = takeWhile (/= 0) $ iterate nextCollatz n
+collatzChainStartingAt :: Integer -> (Integer, Integer)
+collatzChainStartingAt n = (n, s')
+  where s' = genericLength $ takeWhile (/= 0) $ iterate nextCollatz n
 
 limit :: Integer
 limit = 1_000_000