Day 07 - part 1.

app/Main.hs

@@ -30,4 +30,4 @@ import qualified Day24
 import qualified Day25
 
 main :: IO ()
-main = Day06.main
+main = Day07.main

input/07.txt

@@ -0,0 +1,101 @@
+Step G must be finished before step M can begin.
+Step T must be finished before step E can begin.
+Step P must be finished before step M can begin.
+Step V must be finished before step L can begin.
+Step Y must be finished before step B can begin.
+Step K must be finished before step Z can begin.
+Step H must be finished before step I can begin.
+Step D must be finished before step U can begin.
+Step C must be finished before step L can begin.
+Step R must be finished before step Z can begin.
+Step U must be finished before step B can begin.
+Step J must be finished before step M can begin.
+Step M must be finished before step E can begin.
+Step I must be finished before step X can begin.
+Step N must be finished before step O can begin.
+Step S must be finished before step F can begin.
+Step X must be finished before step A can begin.
+Step F must be finished before step Q can begin.
+Step B must be finished before step Z can begin.
+Step Q must be finished before step W can begin.
+Step L must be finished before step W can begin.
+Step O must be finished before step Z can begin.
+Step A must be finished before step Z can begin.
+Step E must be finished before step W can begin.
+Step W must be finished before step Z can begin.
+Step G must be finished before step R can begin.
+Step H must be finished before step A can begin.
+Step A must be finished before step W can begin.
+Step Y must be finished before step D can begin.
+Step O must be finished before step A can begin.
+Step V must be finished before step U can begin.
+Step H must be finished before step W can begin.
+Step K must be finished before step F can begin.
+Step J must be finished before step X can begin.
+Step V must be finished before step R can begin.
+Step Q must be finished before step A can begin.
+Step F must be finished before step B can begin.
+Step G must be finished before step P can begin.
+Step L must be finished before step A can begin.
+Step B must be finished before step Q can begin.
+Step H must be finished before step J can begin.
+Step J must be finished before step L can begin.
+Step F must be finished before step E can begin.
+Step U must be finished before step A can begin.
+Step G must be finished before step Q can begin.
+Step G must be finished before step S can begin.
+Step K must be finished before step J can begin.
+Step N must be finished before step B can begin.
+Step F must be finished before step O can begin.
+Step C must be finished before step Z can begin.
+Step B must be finished before step E can begin.
+Step M must be finished before step S can begin.
+Step A must be finished before step E can begin.
+Step E must be finished before step Z can begin.
+Step K must be finished before step I can begin.
+Step P must be finished before step A can begin.
+Step Y must be finished before step L can begin.
+Step Y must be finished before step J can begin.
+Step G must be finished before step N can begin.
+Step Q must be finished before step L can begin.
+Step D must be finished before step X can begin.
+Step C must be finished before step I can begin.
+Step K must be finished before step B can begin.
+Step N must be finished before step F can begin.
+Step D must be finished before step M can begin.
+Step B must be finished before step A can begin.
+Step U must be finished before step J can begin.
+Step Q must be finished before step Z can begin.
+Step X must be finished before step F can begin.
+Step K must be finished before step X can begin.
+Step U must be finished before step E can begin.
+Step X must be finished before step W can begin.
+Step K must be finished before step Q can begin.
+Step I must be finished before step E can begin.
+Step D must be finished before step J can begin.
+Step P must be finished before step I can begin.
+Step K must be finished before step D can begin.
+Step S must be finished before step X can begin.
+Step C must be finished before step R can begin.
+Step P must be finished before step W can begin.
+Step I must be finished before step O can begin.
+Step S must be finished before step O can begin.
+Step K must be finished before step C can begin.
+Step N must be finished before step Q can begin.
+Step L must be finished before step E can begin.
+Step L must be finished before step Z can begin.
+Step K must be finished before step W can begin.
+Step Y must be finished before step A can begin.
+Step L must be finished before step O can begin.
+Step N must be finished before step W can begin.
+Step R must be finished before step W can begin.
+Step C must be finished before step O can begin.
+Step H must be finished before step X can begin.
+Step V must be finished before step Y can begin.
+Step S must be finished before step W can begin.
+Step V must be finished before step E can begin.
+Step Q must be finished before step E can begin.
+Step P must be finished before step H can begin.
+Step V must be finished before step H can begin.
+Step N must be finished before step Z can begin.
+Step C must be finished before step A can begin.

package.yaml

@@ -23,6 +23,7 @@ dependencies:
 - base >= 4.7 && < 5
 - containers
 - text
+- extra
 
 library:
   source-dirs: src

src/Day07.hs

@@ -1,6 +1,28 @@
 module Day07 (main) where
 
+import Data.Map (Map, fromListWith, fromList, findMin)
+import qualified Data.Map as M (union, null, filter, delete)
+import Data.Set (Set, singleton, empty)
+import qualified Data.Set as S (union, null, delete)
+import Data.Tuple.Extra (second)
+
+parse :: String -> (Char, Char)
+parse str = (str !! 36, str !! 5)
+
+dependencies :: [(Char, Char)] -> Map Char (Set Char)
+dependencies ds =
+    let dependents   = fromListWith S.union . map (second singleton) $ ds
+        independents = fromList . (flip zip) (repeat empty) . snd . unzip $ ds
+    in M.union dependents independents
+
+part1 :: Map Char (Set Char) -> String -> String
+part1 deps str
+    | M.null deps = reverse str
+    | otherwise =
+        let available = fst . findMin . M.filter S.null $ deps
+        in  part1 (fmap (S.delete available) (M.delete available deps)) (available:str)
+
 main :: IO ()
 main = do
-    input <- readFile "input/07.txt"
-    print input
+    input <- map parse . lines <$> readFile "input/07.txt"
+    putStrLn $ part1 (dependencies input) ""