Initial day04

README.md

@@ -7,7 +7,7 @@ These are my attempts on [AoC 2022](https://adventofcode.com/2022/)
 | [01](day01)  |   ⭐   |   ⭐   | Python   |
 | [02](day02)  |   ⭐   |   ⭐   | C        |
 | [03](day03)  |   ⭐   |   ⭐   | Rust     |
-| 04           |        |        |          |
+| [04](day04)  |   ⭐   |   ⭐   | Haskell  |
 | 05           |        |        |          |
 | 06           |        |        |          |
 | 07           |        |        |          |

day04/input_demo.txt

@@ -0,0 +1,6 @@
+2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8

day04/main.hs

@@ -0,0 +1,67 @@
+import Data.Char
+
+main = do  
+  let list = []
+  file <- readFile "input.txt"
+  let inputLines = lines file
+  let pairs = map (splitWhen (==',')) inputLines
+
+  -- Each pair is a set of two numbers separated by a dash
+  let limits = map (map parseRange) pairs
+
+  let containedWithin = map rangeListIsContained limits
+  
+  let containedCount = length $ filter (==True) containedWithin
+  print "Part 1: "
+  print containedCount
+
+  let overlap = map rangeListOverlap limits
+  let overlapCount = length $ filter (==True) overlap
+  print "Part 2: "
+  print overlapCount
+
+
+parseRange :: String -> (Int, Int)
+parseRange pair = do
+  let numbers = splitWhen (=='-') pair
+  let first = read (numbers !! 0) :: Int
+  let second = read (numbers !! 1) :: Int
+  (first, second)
+
+
+-- True if the first range is entirely contained in the second range, or vice versa
+rangeIsContained :: (Int, Int) -> (Int, Int) -> Bool
+rangeIsContained (lo1, hi1) (lo2, hi2)
+  | lo1 <= lo2 && hi1 >= hi2 = True
+  | lo1 >= lo2 && hi1 <= hi2 = True
+  | otherwise = False
+
+-- True if any endpoint of a range is within the other range
+rangeOverlaps :: (Int, Int) -> (Int, Int) -> Bool
+rangeOverlaps (lo1, hi1) (lo2, hi2)
+  | rangeIsContained (lo1, lo1) (lo2, hi2) = True
+  | lo2 >= lo1 && lo2 <= hi1 = True
+  | hi2 >= lo1 && hi2 <= hi1 = True
+  | otherwise = False
+
+
+-- This is mega dirty, should probably be replaced with a smart map.
+rangeListIsContained :: [(Int, Int)] -> Bool
+rangeListIsContained ranges = do
+  let first = ranges !! 0
+  let second = ranges !! 1
+  rangeIsContained first second
+
+rangeListOverlap :: [(Int, Int)] -> Bool
+rangeListOverlap ranges = do
+  let first = ranges !! 0
+  let second = ranges !! 1
+  rangeOverlaps first second
+
+-- Modified from Prelude.words
+splitWhen :: (Char -> Bool) -> String -> [String]
+splitWhen p s = case dropWhile p s of
+  "" -> []
+  s' -> w : splitWhen p s''
+    where (w, s'') = break p s'
+