initial commit

1 files changed, 34 insertions, 0 deletions

diff --git a/2020/09b.hs b/2020/09b.hs
new file mode 100644
index 0000000..a643b29
--- /dev/null
+++ b/2020/09b.hs
@@ -0,0 +1,34 @@
+module Day9B where
+
+import System.Environment (getArgs)
+
+potentialSum :: [Int] -> Int -> [(Int, Int)]
+potentialSum xs t = filter ((== t) . uncurry (+)) [(x, y) | x <- xs, y <- xs, x /= y]
+
+mapSumPrev :: [Int] -> Int -> [[(Int, Int)]]
+mapSumPrev xs l = [potentialSum (take l $ drop (i - l) xs) v | (i, v) <- zip [25..] (drop l xs)]
+
+rangesSummingTo :: [Int] -> Int -> [[Int]]
+rangesSummingTo [] _ = []
+rangesSummingTo xs t = filter ((== t) . sum) $ map (`take` xs) [1..length xs]
+                        ++ rangesSummingTo (drop 1 xs) t
+
+numsFromFile :: String -> IO [Int]
+numsFromFile p = do
+                    c <- readFile p;
+                    return $ map read $ lines c; 
+
+main :: IO ()
+main = do 
+        args <- getArgs;
+        xs <- numsFromFile $ head args;
+
+        let unob = head $ filter (null . fst) $ zip (mapSumPrev xs 25) [25..];
+        let unob_n = xs !! snd unob;
+        putStrLn $ "No way to sum up to " ++ show unob_n;
+
+        let rs = head $ rangesSummingTo xs unob_n;
+        print rs;
+
+        putStrLn $ "Smallest + Largest = " ++ show (minimum rs + maximum rs);
+        return ();