Day 8

aoc2022.cabal

@@ -47,6 +47,7 @@ library
       Day7
       Day7.Interpreter
       Day7.Parser
+      Day8
       Lib
       Shared
   other-modules:
@@ -61,9 +62,12 @@ library
     , heredoc
     , hspec
     , lens
+    , matrix
+    , megaparsec
     , parsec
     , split
     , text
+    , vector
   default-language: Haskell2010
 
 executable aoc2022-exe
@@ -81,9 +85,12 @@ executable aoc2022-exe
     , heredoc
     , hspec
     , lens
+    , matrix
+    , megaparsec
     , parsec
     , split
     , text
+    , vector
   default-language: Haskell2010
 
 test-suite aoc2022-test
@@ -97,6 +104,7 @@ test-suite aoc2022-test
       Day5Spec
       Day6Spec
       Day7Spec
+      Day8Spec
       Paths_aoc2022
   hs-source-dirs:
       test
@@ -109,7 +117,10 @@ test-suite aoc2022-test
     , heredoc
     , hspec
     , lens
+    , matrix
+    , megaparsec
     , parsec
     , split
     , text
+    , vector
   default-language: Haskell2010

package.yaml

@@ -30,6 +30,9 @@ dependencies:
 - lens
 - Ranged-sets
 - parsec
+- matrix
+- vector
+- megaparsec
 
 ghc-options:
 - -Wall

ressources/day08-input

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src/Day8.hs

@@ -0,0 +1,84 @@
+module Day8 (
+  Forest,
+  Visibillity,
+  parseForest,
+  checkVisibility,
+  countVisible,
+  findMaxScenicScore,
+  viewingDistance,
+  day8
+)where
+
+import qualified Data.Matrix as M
+import Data.Matrix ((!))
+import Data.Char (isDigit)
+import qualified Data.Vector as V
+import Data.Monoid (Sum (..), getSum, Product (..), getProduct)
+import Control.Arrow ((>>>))
+
+type Forest = M.Matrix Int
+type Visibillity = M.Matrix Bool
+
+parseForest :: String -> Forest
+parseForest input = M.fromList rows cols asNumbers
+                     where
+                       ls = lines input
+                       cols = length (head ls)
+                       rows = length ls
+                       asNumbers :: [Int]
+                       asNumbers = map (read . (: [])) . filter isDigit $ input
+
+checkAgainstNeighbours :: (Int -> [V.Vector Int] -> a) -> Forest -> M.Matrix a
+checkAgainstNeighbours f forest  = M.matrix (M.nrows forest) (M.ncols forest) check
+  where
+    check(x, y) =
+      let row = M.getRow x forest
+          col = M.getCol y forest
+          -- left and top are reversed to order the as seen from (x,y)
+          left   = V.reverse $ V.take (y - 1) row 
+          right  = V.drop y row
+          top    = V.reverse $ V.take (x - 1) col 
+          bottom = V.drop x col
+          v = forest ! (x,y)
+      in f v [left, right, top, bottom]
+
+checkVisibility :: Forest -> Visibillity
+checkVisibility = checkAgainstNeighbours isVisible
+  where
+    isVisible v = any (all (< v))
+
+countVisible :: Visibillity -> Int
+countVisible vis = getSum $ foldMap (Sum . isTrue) vis
+  where
+    isTrue True = 1
+    isTrue False = 0
+
+checkScenicScores :: Forest -> M.Matrix Int
+checkScenicScores = checkAgainstNeighbours allDistances
+  where
+    allDistances tree neighbors = getProduct $ foldMap (Product . viewingDistance tree) neighbors
+
+viewingDistance :: Int -> V.Vector Int -> Int
+viewingDistance treeHeight neighbors
+  | V.length neighbors == 0 = 0
+  | V.head neighbors >= treeHeight = 1
+  | V.head neighbors < treeHeight = 1 + viewingDistance treeHeight (V.tail neighbors)
+  | otherwise = 0
+
+findMaxScenicScore :: Forest -> Int
+findMaxScenicScore forest = maximum $ M.toList scores
+  where
+    scores = checkScenicScores forest
+
+day8 :: IO ()
+day8 = do
+   input <- readFile "ressources/day08-input"
+   putStrLn "Day8"
+   let forest = parseForest input
+   let visibleTrees = checkVisibility >>>
+                      countVisible $ forest
+   putStrLn ("Number of visible trees is " ++ show visibleTrees)
+   let highestScenicScore = findMaxScenicScore forest
+   putStrLn ("Highest scenic score is " ++ show highestScenicScore)
+   
+

src/Lib.hs

@@ -9,6 +9,7 @@ import Day4
 import Day5
 import Day6
 import Day7
+import Day8
 
 someFunc :: IO ()
 someFunc = do
@@ -25,5 +26,7 @@ someFunc = do
   day6
   putStrLn "-----------"
   day7
+  putStrLn "-----------"
+  day8
   
 

test/Day6Spec.hs

@@ -2,7 +2,6 @@ module Day6Spec (spec) where
 
 import Test.Hspec
 import Day6
-import qualified Data.Sequence as S
 
 spec :: Spec
 spec =

test/Day8Spec.hs

@@ -0,0 +1,65 @@
+{-# LANGUAGE QuasiQuotes #-}
+module Day8Spec (spec) where
+
+import Test.Hspec
+import Text.Heredoc
+import Control.Arrow ((>>>))
+
+import qualified Data.Matrix as M
+import qualified Data.Vector as V
+import Day8
+
+testInput :: String
+testInput = [str|30373
+                |25512
+                |65332
+                |33549
+                |35390
+                |]
+
+testVisibility :: Visibillity
+testVisibility = M.fromList 5 5
+  [x,x,x,x,x,
+   x,x,x,o,x,
+   x,x,o,x,x,
+   x,o,x,o,x,
+   x,x,x,x,x
+  ]
+  where
+    x = True
+    o = False
+
+smallForest :: String
+smallForest = [str|1234
+                  |5678
+                  |9012
+                  |]
+
+parsedSmallForest :: Forest
+parsedSmallForest = M.fromList 3 4 $ [1..9] ++ [0,1,2]
+
+spec :: Spec
+spec =
+  describe "Day8" $ do
+    describe "Part1" $ do
+      it "parses a forest" $ do
+        parseForest smallForest `shouldBe` parsedSmallForest
+      it "checks visibility" $ do
+        let forest = parseForest testInput
+        checkVisibility forest `shouldBe` testVisibility
+      it "counts visible things" $ do
+        let v = parseForest >>>
+                checkVisibility >>>
+                countVisible $ testInput
+        v `shouldBe` 21
+    describe "Part2" $ do
+      it "calculates viewing distance from height" $ do
+        viewingDistance 5 (V.fromList [3]) `shouldBe` 1
+        viewingDistance 5 (V.fromList [5,2]) `shouldBe` 1
+        viewingDistance 5 (V.fromList [1,2]) `shouldBe` 2
+        viewingDistance 5 (V.fromList [3,5,3]) `shouldBe` 2
+      it "calculates the scenic score" $ do
+        let s = parseForest >>>
+                findMaxScenicScore $ testInput
+        s `shouldBe` 8
+