Added day 1 and 2

1/example.txt

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+199
+200
+208
+210
+200
+207
+240
+269
+260
+263

1/solution.hs

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+import Data.List
+
+main :: IO ()
+main = readFile "1/input.txt" >>= print . solve . parse . lines
+
+parse :: [String] -> [Int]
+parse = map read
+
+solve :: [Int] -> (Int, Int)
+solve input = (f input, g input)
+    where f = countInc
+          g = countInc . map sum . slide 3
+
+countInc :: [Int] -> Int
+countInc (a : rest @ (b : _))
+    | a < b     = countInc rest + 1
+    | otherwise = countInc rest
+countInc _      = 0
+
+slide :: Int -> [Int] -> [[Int]]
+slide _ []   = []
+slide n list = take n list : slide n (tail list)

2/example.txt

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+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2

2/solution.hs

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+main :: IO ()
+main = readFile "2/input.txt" >>= print . solve . parse . lines
+
+parse :: [String] -> [Instruction]
+parse = map (parseLine . words)
+
+solve :: [Instruction] -> (Int,Int)
+solve input = (f input, g input)
+    where f = uncurry (*) . simulate Abs
+          g = uncurry (*) . simulate (Aim 0)
+
+data Nav = Aim Int 
+         | Abs
+
+data Instruction = Forward Int
+                 | Down Int
+                 | Up Int
+
+parseLine :: [String] -> Instruction
+parseLine [ s, x ]
+    | s == "forward" = Forward n
+    | s == "down"    = Down n
+    | s == "up"      = Up n
+    where
+        n = read x
+
+simulate :: Nav -> [Instruction] -> (Int,Int)
+simulate nav = iter nav (0,0)
+
+iter :: Nav -> (Int,Int) -> [Instruction] -> (Int,Int)
+iter _ r [] = r
+iter Abs (x,y) (i:is) = case i of
+        Forward n -> iter Abs (x+n,y)
+        Down n    -> iter Abs (x,y+n)
+        Up n      -> iter Abs (x,y-n)
+    $ is
+iter (Aim a) (x,y) (i:is) = case i of
+        Forward n -> iter (Aim a) (x+n,y+(a*n))
+        Down n    -> iter (Aim (a+n)) (x,y)
+        Up n      -> iter (Aim (a-n)) (x,y)
+    $ is

README.md

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+# Advent of Code 2021

shell.nix

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+{ pkgs ? import <nixpkgs> {} }: pkgs.mkShell {
+    nativeBuildInputs = with pkgs; [
+        haskell-language-server
+        cabal-install
+        ghc
+    ];
+}