Day 7, parts 1 & 2: Initial solutions.

Day7/Part1.hs

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+#! /usr/bin/env stack
+-- stack --resolver lts-12.20 --install-ghc script
+{-# LANGUAGE ViewPatterns #-}
+module Main where
+
+import Data.Function (fix)
+import qualified Data.List as L
+import qualified Data.Set  as S
+import qualified Data.Map  as M
+
+main :: IO ()
+main = interact $ (. (M.unionsWith (<>) . map parseLine . lines)) $ fix $ \repeat depSets ->
+   if M.null depSets then "" else let
+      (noDep, _) = M.findMin $ M.filter S.null depSets
+      depSets' = M.map (S.delete noDep) (M.delete noDep depSets)
+   in noDep : repeat depSets'
+
+parseLine :: String -> M.Map Char (S.Set Char)
+parseLine (words -> ws) =
+       M.unionWith (<>) (M.singleton req S.empty)
+                        (M.singleton step (S.singleton req))
+   where
+      req  = (head $ ws !! 1)
+      step = (head $ ws !! 7)
+

Day7/Part2.hs

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+#! /usr/bin/env stack
+-- stack --resolver lts-12.20 --install-ghc script
+{-# LANGUAGE ViewPatterns #-}
+module Main where
+
+import Control.Arrow ((&&&))
+import qualified Data.List as L
+import qualified Data.Set  as S
+import qualified Data.Map  as M
+
+import Debug.Trace
+
+main :: IO ()
+main = interact $ show . simulate (-1) [] . parseInput
+
+simulate :: Int -> [(Char, Int)] -> M.Map Char (S.Set Char) -> Int
+simulate t ws depSets = traceShow (t, ws) $
+      if null ws && M.null depSets then t
+      else simulate (t+1) ws'' depSets''
+   where
+      (ws', S.fromList . fmap fst -> finished) =
+          L.partition ((> 0) . snd) $ fmap (fmap (subtract 1)) ws
+      depSets' = M.map (`S.difference` finished) depSets
+      starting = take (5 - length ws') . L.sort . M.keys . M.filter S.null $ depSets'
+      stepTime c = 60 + (fromEnum c - fromEnum 'A' + 1)
+      ws'' = ws' ++ fmap (id &&& stepTime) starting
+      depSets'' = flip (foldr M.delete) starting depSets'
+
+parseInput :: String -> M.Map Char (S.Set Char)
+parseInput = M.unionsWith (<>) . fmap parseLine . lines
+   where
+      parseLine (words -> (_:(req:_):_:_:_:_:_:(step:_):_)) =
+         M.fromList [(req, S.empty), (step, S.singleton req)]

Day7/input.txt

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