1 files changed, 35 insertions, 0 deletions

diff --git a/execs/Day09.hs b/execs/Day09.hs
new file mode 100644
index 0000000..e2e5fd4
--- /dev/null
+++ b/execs/Day09.hs
@@ -0,0 +1,35 @@
+
+module Main where
+
+import Utils
+import Data.List (inits, tails, find)
+import Data.Bifunctor
+
+parseLine :: String -> Int
+parseLine = read
+
+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
+
+
+findWeakness :: [[Int]] -> Int -> Int
+findWeakness subs target = mn + mx
+    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
+    print target
+    print $ findWeakness (sublists n) target