From 644c38de8b633dc5e03bff5216f68b2bfde4a645 Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Wed, 9 Dec 2020 11:03:39 +0530
Subject: add initial solution for day09

---
 execs/Day08.hs |  4 ++--
 execs/Day09.hs | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 execs/Day09.hs

(limited to 'execs')

diff --git a/execs/Day08.hs b/execs/Day08.hs
index 7d3fce8..6546990 100644
--- a/execs/Day08.hs
+++ b/execs/Day08.hs
@@ -40,6 +40,6 @@ genAll (acc:rest) = map (acc:) $ genAll rest
 main :: IO ()
 main = do
     n <- map (parseLine . words) . lines <$> readFile "input/08"
-    let solve1 = run 0 0 Set.empty . Map.fromList . zip [0..] 
+    let solve1 = run 0 0 mempty . Map.fromList . zip [0..] 
     print $ solve1 n
-    print $ solve1 $ head $ filter (doesEnd 0 0 Set.empty . Map.fromList . zip [0..]) $ genAll n
+    print $ solve1 $ head $ filter (doesEnd 0 0 mempty . Map.fromList . zip [0..]) $ genAll n
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
-- 
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