Add 2020 day 5

haskellAoC/src/Y2020/Day05.hs

@@ -0,0 +1,39 @@
+module Y2020.Day05 (y20day05) where
+
+import Data.List
+
+parseRow :: [Char] -> Int
+parseRow ('B':[]) = 1
+parseRow ('F':[]) = 0
+parseRow ('B':xs) = 1 + 2 * parseRow xs
+parseRow ('F':xs) = 2 * parseRow xs
+
+parseCol :: [Char] -> Int
+parseCol "RRR" = 7
+parseCol "RRL" = 6
+parseCol "RLR" = 5
+parseCol "RLL" = 4
+parseCol "LRR" = 3
+parseCol "LRL" = 2
+parseCol "LLR" = 1
+parseCol "LLL" = 0
+
+parseInput :: [Char] -> (Int, Int)
+parseInput input = (row, col)
+  where row = parseRow $ reverse $ (take 7 input)
+        col = parseCol $ drop 7 input
+
+computeSeatId :: (Int, Int) -> Int
+computeSeatId (row, col) = row * 8 + col
+
+findMissingId :: [Int] -> Int
+findMissingId (x:x2:xs)
+  | x2 == x + 1 = findMissingId (x2:xs)
+  | otherwise = x + 1
+findMissingId _ = -1
+
+y20day05 :: [String] -> (String, String)
+y20day05 input = (part1, part2)
+  where part1 = show $ maximum $ map computeSeatId parsedInput
+        part2 = show $ findMissingId $ sort $ map computeSeatId parsedInput
+        parsedInput = map parseInput input

haskellAoC/src/Y2020/Days.hs

@@ -4,6 +4,7 @@ import Y2020.Day01
 import Y2020.Day02
 import Y2020.Day03
 import Y2020.Day04
+import Y2020.Day05
 
 
 year2020 :: String -> [String] -> (String, String)
@@ -11,3 +12,4 @@ year2020 "01" = y20day01
 year2020 "02" = y20day02
 year2020 "03" = y20day03
 year2020 "04" = y20day04
+year2020 "05" = y20day05