From a961cfecaf9c21f41dfabe8d105512326b5881e0 Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Sun, 13 Dec 2020 12:05:25 +0530
Subject: add day13, crt from rosetta

---
 execs/Day13.hs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 execs/Day13.hs

(limited to 'execs')

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
-- 
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