add day13, crt from rosetta

1 files changed, 25 insertions, 0 deletions

diff --git a/execs/Day13.hs b/execs/Day13.hs
new file mode 100644
index 0000000..07d379d
--- /dev/null
+++ b/execs/Day13.hs
@@ -0,0 +1,25 @@
+module Main where
+
+import Utils
+import Data.List.Split
+import Data.Tuple
+import Data.List (sortOn)
+import Data.Bifunctor
+import Control.Monad (zipWithM, ap)
+
+earliest :: Int -> [Int] -> Int
+earliest start ls = t * b
+    where (t, b) = minimum $ map swap $ zip `ap` map (mod start) $ ls
+
+gold :: [(Int, Int)] -> Int
+gold ls = t
+    where Just t = chineseRemainder ls
+
+main :: IO ()
+main = do
+    n <- lines <$> readFile "input/13"
+    let start   = read (head n) :: Int
+        departs = map read $ filter (/= "x") $ splitOn "," (last n)
+        offs    = map (bimap negate read) $ filter ((/= "x") . snd) $ zip [0..] $ splitOn "," (last n)
+    print $ earliest (negate start) departs
+    print $ gold offs