Add 2020 day 16

haskellAoC/src/Y2020/Day16.hs

@@ -0,0 +1,63 @@
+module Y2020.Day16 (y20day16) where
+
+import Data.List.Split
+import Data.List
+
+data Field = Field {label :: String, validateFn :: Int -> Bool}
+
+parseField :: String -> Field
+parseField input = Field lbl validateInput
+  where input'   = splitOn ":" input
+
+        lbl             = input' !! 0
+        [p1, "or", p2]  = words $ input' !! 1
+
+        validateInput i = (validateRange p1 i) || (validateRange p2 i)
+        validateRange strRange i = i >= mini && i <= maxi
+          where [mini, maxi] = map read $ splitOn "-" strRange
+
+checkFields :: [Field] -> Int -> [String]
+checkFields [] _ = []
+checkFields ((Field lbl v):fs) tkt
+  | (v tkt) == True = lbl:(checkFields fs tkt)
+  | otherwise = checkFields fs tkt
+
+parseTicket :: String -> [Int]
+parseTicket s = map read $ splitOn "," s
+
+ticketIsValid :: [Field] -> [Int] -> Bool
+ticketIsValid valids fields = (== 0) . length $ filter ((== 0) . length) $ map (checkFields valids) fields
+
+-- validation function
+-- values (without indices)
+-- valid indices
+validIndices :: (Int -> Bool) -> [Int] -> [Int]
+validIndices fn tkt = map fst $ filter (\(k, v) -> v == True) $ zip (iterate (+1) 0) $ map fn tkt
+
+fieldIndices :: [[Int]] -> Field -> [Int]
+fieldIndices tkts (Field _ fn) = common $ map (validIndices fn) tkts
+  where common [] = []
+        common (l1:ls) = foldl intersect l1 ls
+
+getFieldsIndices :: [(String, [Int])] -> [(String, Int)]
+getFieldsIndices [] = []
+getFieldsIndices input = (lbl, index):remaining
+  where getFirstOnlyIndex ((l, is):t)
+          | length is == 1 = (l, head is)
+          | otherwise = getFirstOnlyIndex t
+        (lbl, index) = getFirstOnlyIndex input
+        remaining = getFieldsIndices $ map filterOutIndex $ filter (\(l, _) -> l /= lbl) input
+        filterOutIndex (l, is') = (l, filter (\i -> i /= index) is')
+
+y20day16 :: [String] -> (String, String)
+y20day16 input = (part1, part2)
+  where part1 = show $ sum $ filter (\v -> (== 0) $ length $ checkFields fields v) $ concat nearbyTickets
+        part2 = show $ product $ map ((!!) myTicket) $ map snd $ filter (\(l, _) -> "departure" `isPrefixOf` l) $ fieldsIndices
+
+        [raw_fields, raw_myTicket, raw_nearbyTickets] = splitOn [""] input
+        fields = map parseField raw_fields
+        myTicket = parseTicket $ raw_myTicket !! 1
+        nearbyTickets = map parseTicket $ tail $ raw_nearbyTickets
+
+        validNearbyTickets = filter (ticketIsValid fields) nearbyTickets
+        fieldsIndices = getFieldsIndices $ map (\f -> (label f, fieldIndices validNearbyTickets f)) $ fields

haskellAoC/src/Y2020/Days.hs

@@ -15,6 +15,7 @@ import Y2020.Day12
 import Y2020.Day13
 import Y2020.Day14
 import Y2020.Day15
+import Y2020.Day16
 
 year2020 :: String -> [String] -> (String, String)
 year2020 "01" = y20day01
@@ -32,3 +33,4 @@ year2020 "12" = y20day12
 year2020 "13" = y20day13
 year2020 "14" = y20day14
 year2020 "15" = y20day15
+year2020 "16" = y20day16