From ac3191ae40b8df0873f2e04f5bc1017322941b5d Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Wed, 9 Dec 2020 11:43:55 +0530
Subject: be more <<<functional>>>

---
 execs/Day09.hs | 17 +++++------------
 lib/Utils.hs   |  4 ++++
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/execs/Day09.hs b/execs/Day09.hs
index e2e5fd4..f1c41f2 100644
--- a/execs/Day09.hs
+++ b/execs/Day09.hs
@@ -2,7 +2,7 @@
 module Main where
 
 import Utils
-import Data.List (inits, tails, find)
+import Data.List (inits, tails, find, sort)
 import Data.Bifunctor
 
 parseLine :: String -> Int
@@ -12,24 +12,17 @@ doCheck :: [Int] -> Int -> Bool
 doCheck preamble target = target `elem` p
     where p = [x + y | x <- preamble, y <- preamble, x /= y]
 
-checkAll :: [Int] -> [Int] -> [(Int, Bool)]
-checkAll preamble [x] = [(x, doCheck preamble x)]
-checkAll preamble@(p:ps) (x:xs) = (x, doCheck preamble x) : checkAll (ps++[x]) xs
-
+checkAll :: [[Int]] -> [Int] -> [(Int, Bool)]
+checkAll = zipWith (\p t -> (t, doCheck p t)) 
 
 findWeakness :: [[Int]] -> Int -> Int
-findWeakness subs target = mn + mx
+findWeakness subs target = minimum t + maximum t
     where Just t = find ((== target) . sum) subs
-          mn = minimum t
-          mx = maximum t
  
 main :: IO ()
 main = do
     n <- map parseLine . lines <$> readFile "input/09"
     let preambleLen = 25
-        Just (target, _) = find (not . snd) 
-            $ uncurry checkAll
-            $ bimap (take preambleLen) (drop preambleLen) 
-            $ (,) n n
+        Just (target, _) = find (not . snd) $ checkAll (windows preambleLen n) (drop preambleLen n)
     print target
     print $ findWeakness (sublists n) target
diff --git a/lib/Utils.hs b/lib/Utils.hs
index 89b1bd3..1381f16 100644
--- a/lib/Utils.hs
+++ b/lib/Utils.hs
@@ -6,6 +6,7 @@ module Utils ( binaryToInt
              , (&+)
              , howMany
              , sublists
+             , windows
              ) where 
 
 import Data.Char (digitToInt)
@@ -39,3 +40,6 @@ howMany predicate = length . filter predicate
 
 sublists :: [a] -> [[a]]
 sublists = concatMap inits . tails
+
+windows :: Int -> [a] -> [[a]]
+windows m = foldr (zipWith (:)) (repeat []) . take m . tails
-- 
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