Day 4 Part 2

04/Main.idr

@@ -20,6 +20,10 @@ parseRange str =
 contains : Range -> Range -> Bool
 contains outer inner = (start outer <= start inner) && (end outer >= end inner)
 
+-- Returns true if the first range contains part of the second
+overlaps : Range -> Range -> Bool
+overlaps outer inner = start outer <= start inner && end outer >= start inner
+
 record RangePair where
   constructor MkRangePair
   first, second : Range
@@ -38,6 +42,10 @@ parseRangePair str =
 doesContain : RangePair -> Bool
 doesContain pair = contains (first pair) (second pair) || contains (second pair) (first pair)
 
+-- Returns true if one of the ranges overlaps the other
+doesOverlap : RangePair -> Bool
+doesOverlap pair = overlaps (first pair) (second pair) || overlaps (second pair) (first pair)
+
 
 main : IO ()
 main =
@@ -46,6 +54,9 @@ main =
        Right content =>
          let pairs = catMaybes . map parseRangePair . lines $ content
              containsCount = length . filter doesContain $ pairs
+             overlapsCount = length . filter doesOverlap $ pairs
          in do putStr "Part 1: "
                printLn containsCount
+               putStr "Part 2: "
+               printLn overlapsCount
        Left err => printLn err