From 5eb58ad076f2cd435b11b140820da224b60b73d5 Mon Sep 17 00:00:00 2001
From: Aria <me@aria.rip>
Date: Mon, 2 Jan 2023 21:58:56 +0000
Subject: initial commit

---
 2020/07a.hs | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 2020/07a.hs

(limited to '2020/07a.hs')

diff --git a/2020/07a.hs b/2020/07a.hs
new file mode 100644
index 0000000..32c4aaf
--- /dev/null
+++ b/2020/07a.hs
@@ -0,0 +1,36 @@
+module Day7A where
+
+import System.Environment (getArgs)
+import Text.Regex.PCRE
+
+type Rule = (String, [(Int, String)])
+
+parseRule :: String -> Rule
+parseRule xs = (parent, children)
+                where parentMatch = xs =~ "^([a-z ]*) bag" :: [[String]]
+                      parent = head parentMatch!!1
+                      childrenMatch = xs =~ "([0-9]+) ([a-z ]*) bag" :: [[String]]
+                      childrenNs = map (read . (!! 1)) childrenMatch
+                      childrenNames = map (!! 2) childrenMatch 
+                      children = zip childrenNs childrenNames
+
+-- Keep applying f to a until the output stops changing
+untilUnchanged :: Eq a => (a -> a) -> a -> a
+untilUnchanged f a | n /= a    = untilUnchanged f n
+                   | otherwise = n
+                     where n = f a
+
+-- Add the bags that can contain these bags to the list
+addParents :: [Rule] -> [String] -> [String]
+addParents rs xs = map fst $ filter (\(n, cs) -> n `elem` xs || any (`elem` map snd cs) xs) rs
+
+-- Usage: runghc --ghc-arg="-package regex-pcre-builtin" 7a.hs inputs/day7
+main :: IO ()
+main = do 
+        args <- getArgs;
+        content <- readFile $ head args;
+        let rules = map parseRule $ lines content;
+        let topLevels = untilUnchanged (addParents rules) ["shiny gold"]
+        print topLevels;
+        print $ length topLevels - 1;
+        return ();
\ No newline at end of file
-- 
cgit v1.2.3