From bab470906e1c61176c3002698e58980a8d5787e4 Mon Sep 17 00:00:00 2001
From: Felix Albrigtsen <felixalbrigtsen@gmail.com>
Date: Sun, 4 Dec 2022 13:29:07 +0100
Subject: [PATCH] Improve day04

---
 day04/main.hs | 31 +++++++++----------------------
 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/day04/main.hs b/day04/main.hs
index 2863145..3b073e0 100644
--- a/day04/main.hs
+++ b/day04/main.hs
@@ -4,23 +4,25 @@ main = do
   let list = []
   file <- readFile "input.txt"
   let inputLines = lines file
-  let pairs = map (splitWhen (==',')) inputLines
+  let stringpairs = map (splitWhen (==',')) inputLines
 
-  -- Each pair is a set of two numbers separated by a dash
-  let limits = map (map parseRange) pairs
+  let listpairs = map (map parseRange) stringpairs
+  let pairs = map (\x -> (head x, last x)) listpairs
 
-  let containedWithin = map rangeListIsContained limits
-  
+  -- Each line of input has now gone from "1-2,3-4" to ((1,2),(3,4))
+
+  let containedWithin = map (uncurry rangeIsContained) pairs
   let containedCount = length $ filter (==True) containedWithin
   print "Part 1: "
   print containedCount
 
-  let overlap = map rangeListOverlap limits
+  let overlap = map (uncurry rangeOverlaps) pairs
   let overlapCount = length $ filter (==True) overlap
   print "Part 2: "
   print overlapCount
 
 
+-- "1-3" -> (1,3)
 parseRange :: String -> (Int, Int)
 parseRange pair = do
   let numbers = splitWhen (=='-') pair
@@ -28,7 +30,6 @@ parseRange pair = do
   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)
@@ -36,7 +37,7 @@ rangeIsContained (lo1, hi1) (lo2, hi2)
   | lo1 >= lo2 && hi1 <= hi2 = True
   | otherwise = False
 
--- True if any endpoint of a range is within the other range
+-- True if any part of the two ranges overlap
 rangeOverlaps :: (Int, Int) -> (Int, Int) -> Bool
 rangeOverlaps (lo1, hi1) (lo2, hi2)
   | rangeIsContained (lo1, lo1) (lo2, hi2) = True
@@ -44,20 +45,6 @@ rangeOverlaps (lo1, hi1) (lo2, hi2)
   | 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