parser

adventofcode.cabal

@@ -35,6 +35,7 @@ library
       Day5
       Day6
   other-modules:
+      Day7
       Paths_adventofcode
   build-depends:
       base >=4.7 && <5
@@ -43,6 +44,7 @@ library
     , foldl
     , text
     , array
+    , parsec
   default-language: Haskell2010
 
 executable adventofcode-exe

package.yaml

@@ -26,6 +26,7 @@ library:
   - foldl
   - text
   - array
+  - parsec
 executables:
   adventofcode-exe:
     main: Main.hs

src/Day7.hs

@@ -0,0 +1,135 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-|
+description:
+
+--- Day 7: Recursive Circus ---
+
+Wandering further through the circuits of the computer, you come upon a tower of
+programs that have gotten themselves into a bit of trouble. A recursive
+algorithm has gotten out of hand, and now they're balanced precariously in a
+large tower.
+
+One program at the bottom supports the entire tower. It's holding a large disc,
+and on the disc are balanced several more sub-towers. At the bottom of these
+sub-towers, standing on the bottom disc, are other programs, each holding their
+own disc, and so on. At the very tops of these sub-sub-sub-...-towers, many
+programs stand simply keeping the disc below them balanced but with no disc of
+their own.
+
+You offer to help, but first you need to understand the structure of these
+towers. You ask each program to yell out their name, their weight, and (if
+they're holding a disc) the names of the programs immediately above them
+balancing on that disc. You write this information down (your puzzle input).
+Unfortunately, in their panic, they don't do this in an orderly fashion; by the
+time you're done, you're not sure which program gave which information.
+
+For example, if your list is the following:
+
+pbga (66)
+xhth (57)
+ebii (61)
+havc (66)
+ktlj (57)
+fwft (72) -> ktlj, cntj, xhth
+qoyq (66)
+padx (45) -> pbga, havc, qoyq
+tknk (41) -> ugml, padx, fwft
+jptl (61)
+ugml (68) -> gyxo, ebii, jptl
+gyxo (61)
+cntj (57)
+
+...then you would be able to recreate the structure of the towers that looks
+like this:
+
+
+                gyxo
+              /
+         ugml - ebii
+       /      \
+      |         jptl
+      |
+      |         pbga
+     /        /
+tknk --- padx - havc
+     \        \
+      |         qoyq
+      |
+      |         ktlj
+       \      /
+         fwft - cntj
+              \
+                xhth
+
+In this example, tknk is at the bottom of the tower (the bottom program), and is
+holding up ugml, padx, and fwft. Those programs are, in turn, holding up other
+programs; in this example, none of those programs are holding up any other
+programs, and are all the tops of their own towers. (The actual tower balancing
+in front of you is much larger.)
+
+Before you're ready to help them, you need to make sure your information is
+correct. What is the name of the bottom program?
+
+
+
+|-}
+module Day7 where
+
+import           Protolude
+
+import qualified Data.Set as Set
+import           Text.Parsec
+
+testInput :: Text
+testInput =  "pbga (66)\n\
+             \xhth (57)\n\
+             \ebii (61)\n\
+             \havc (66)\n\
+             \ktlj (57)\n\
+             \fwft (72) -> ktlj, cntj, xhth\n\
+             \qoyq (66)\n\
+             \padx (45) -> pbga, havc, qoyq\n\
+             \tknk (41) -> ugml, padx, fwft\n\
+             \jptl (61)\n\
+             \ugml (68) -> gyxo, ebii, jptl\n\
+             \gyxo (61)\n\
+             \cntj (57)"
+
+data Node = Node { name   :: Text
+                 , weight :: Int
+                 , sons :: [Text]
+                 } deriving (Eq, Ord,Show)
+type Nodes = [Node]
+
+parseInput :: IO Nodes
+parseInput = do
+  str <- readFile "inputs/day7.txt"
+  return $ either (const empty) identity (parseNodes str)
+
+parseNodes :: Text -> Either ParseError Nodes
+parseNodes = parse nodes "Nodes"
+
+nodes :: Parsec Text () Nodes
+nodes = many1 parseNode
+
+int :: Parsec Text () Int
+int = do
+  str <- many1 digit
+  return $ fromMaybe 0 (reads str & head & fmap fst)
+
+sonsP :: Parsec Text () [Text]
+sonsP = do
+  c <- anyChar
+  if c == '\n'
+    then return []
+    else do
+      string "-> "
+      fmap toS (many1 letter) `sepBy` string ", " <* char '\n'
+
+parseNode :: Parsec Text () Node
+parseNode =
+  Node <$> fmap toS (many1 letter) <* char ' '
+       <*> (char '(' *> int <* char ')')
+       <*> sonsP
+