2021 (and 2019): Day 1

Author: emptyflask

2019/01/input.txt

@@ -0,0 +1,100 @@
+74767
+108567
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+56709

2019/day01.hs

@@ -0,0 +1,15 @@
+main :: IO ()
+main = do
+  input <- readFile "./01/input.txt"
+  let list = read <$> lines input
+  print $ "Part 1: " <> show (solve1 list)
+  print $ "Part 2: " <> show (solve2 list)
+
+solve1 = sum . map fuelForMass
+solve2 = sum . map fuelForMassAndFuel
+
+fuelForMass :: (Integral a) => a -> a
+fuelForMass n = (n `div` 3) - 2
+
+fuelForMassAndFuel :: (Integral a) => a -> a
+fuelForMassAndFuel = sum . takeWhile (> 0) . drop 1 . iterate fuelForMass

2021/01/input.txt

@@ -0,0 +1,20 @@
+import           Data.List (tails)
+
+main :: IO ()
+main = do
+  input <- readFile "./01/input.txt"
+  let list = read <$> lines input
+  print $ "Part 1: " <> show (solve1 list)
+  print $ "Part 2: " <> show (solve2 list)
+
+solve1 :: [Int] -> Int
+solve1 = length . filter (uncurry (<)) . pairs
+
+solve2 :: [Int] -> Int
+solve2 input = length . filter (uncurry (<)) $ pairs (map sum . windows 3 $ input)
+
+pairs :: [a] -> [(a,a)]
+pairs xs@(_:xs') = zip xs xs'
+
+windows :: Int -> [a] -> [[a]]
+windows m = foldr (zipWith (:)) (repeat []) . take m . tails

2021/day01.hs

@@ -0,0 +1,3 @@
+cradle:
+  direct:
+    arguments: []

hie.yaml

@@ -1,3 +1,10 @@
+# Advent of Code 2021
+
+## Day 1:
+
+The `windows` function from last year (day 9) ended up being useful already!
+
+
 # Advent of Code 2020
 
 ## Days 1 - 7:
@@ -102,7 +109,7 @@ against the full input was successful as well, and instantaneous.
 Sort of a game of life simulation but with seating charts. As with all of these
 I'm sure my solution is naive and slow, and I'm working on a rewrite before I
 complete the second part...
-
+https://stackoverflow.com/questions/7442892/repeatedly-applying-a-function-until-the-result-is-stable
 
 ## Day 12:
 
@@ -113,3 +120,11 @@ applying ship instructions in reverse -- this actually worked for part one, but
 since the instructions in part two are order dependant, it was completely wrong
 even on the first instruction. I finally realized my mistake after stepping
 through the solver function with `Debug.Trace`.
+
+
+# Advent of Code 2019
+
+## Day 1:
+
+Did this as a warm-up right before the 2021 AoC opened, initially in the REPL.
+I haven't written any Haskell in 9 months besides messing with [xmonad](https://github.com/xmonad/xmonad).