From 9ca0d11cb692f6ce3e7d4a23d199ccd5da83fb8a Mon Sep 17 00:00:00 2001
From: Riley Apeldoorn <me@riley.lgbt>
Date: Fri, 10 Dec 2021 22:18:58 +0100
Subject: [PATCH] =?UTF-8?q?Day=205:=20It's=20Finally=20Fast=20=E2=84=A2?=
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---
 5/solution.hs | 92 +++++++++++++++------------------------------------
 1 file changed, 26 insertions(+), 66 deletions(-)

diff --git a/5/solution.hs b/5/solution.hs
index ac4d18a..df404d9 100644
--- a/5/solution.hs
+++ b/5/solution.hs
@@ -1,78 +1,38 @@
 import Data.List
 import Data.List.Split
-import Control.Monad (join)
-import Control.Concurrent
+import Data.Char (isDigit)
 
 main :: IO ()
-main = do 
-    input <- readFile "5/example.txt" 
-    let x = parse $ lines input
+main = do
+    input <- readFile "5/riley.txt"
+    let x = parse <$> lines input
     print $ f x
     print $ g x
     where
-        f = length . nub . solve . filter (not . diagonal)
-        g = length . nub . solve
+        f = solve . filter (not . diagonal)
+        g = solve
 
-parse :: [String] -> [(Point,Point)]
-parse = map (parseLine . words)
+-- | Extract all the numbers from the given string
+parse :: String -> [Int]
+parse = map read . wordsBy (not . isDigit)
 
-parseLine :: [String] -> (Point,Point)
-parseLine [ s, "->", e ] = (a, b)
-    where a = parseCoord s
-          b = parseCoord e
+-- | Determine if the given line is diagonal.
+diagonal :: [Int] -> Bool
+diagonal [ x1, y1, x2, y2 ] = x1 /= x2 && y1 /= y2
 
-toRange :: (Point,Point) -> [Point]
-toRange (a @ (xa,ya), b @ (xb,yb))
-    | diagonal (a,b) = makeDiagonal a b
-    | otherwise      = [ (x,y) | x <- [ x1 .. x2 ], y <- [ y1 .. y2 ] ]
-    where
-        x1 = min xa xb
-        x2 = max xa xb
-        y1 = min ya yb
-        y2 = max ya yb
+solve :: [[Int]] -> Int
+solve = length . filter ((>= 2) . length) . group . sort . (>>= range)
 
-parseCoord :: String -> (Int,Int)
-parseCoord l = (head n, last n)
-    where
-        n = map read . wordsBy (== ',') $ l
-
-solve :: [(Point, Point)] -> [Point]
-solve [_] = []
-solve (p:ps) = overlapping' p ps ++ solve ps
-
-overlapping' :: (Point, Point) -> [(Point, Point)] -> [Point]
-overlapping' _ [] = []
-overlapping' p1 (p2:ps) = overlap p1 p2 ++ overlapping' p1 ps
-
-diagonal :: (Point,Point) -> Bool
-diagonal (a,b) = xof a /= xof b && yof a /= yof b
-
-type Point = (Int,Int)
-
-xof :: Point -> Int
-xof = fst
-
-yof :: Point -> Int
-yof = snd
-
-overlap :: (Point,Point) -> (Point,Point) -> [Point]
-overlap a @ (sa,ea) b @ (sb,eb) 
-    | x && y    = toRange a `intersect` toRange b
-    | otherwise = []
-    where
-        x = xof sa >= xof sb || xof sa <= xof sb
-        y = yof sa >= yof sb || yof sa <= yof sb
-
-makeDiagonal :: (Int, Int) -> (Int, Int) -> [(Int, Int)]
-makeDiagonal (a, b) (c, d)
-    | (a > c && b > d) || (a < c && b < d) = 
-        let x1 = min a c
-            x2 = max a c
-            y1 = min b d
-        in [(x1 + i, y1 + i) | i <- [0..(x2 - x1)]]
-    | otherwise = 
-        let x1 = min a c
-            x2 = max a c
-            y1 = max b d
-        in [(x1 + i, y1 - i) | i <- [0..(x2 - x1)]]
+-- | Transform a line to a list of points on that line.
+range :: [Int] -> [(Int,Int)]
+range [ x1, y1, x2, y2 ]
+    | x1 == x2  = [ (x1,y) | y <- ys ]
+    | y1 == y2  = [ (x,y1) | x <- xs ]
+    | otherwise = zip xs ys
+    where xs = gen x1 x2
+          ys = gen y1 y2
 
+-- | Generate a list of numbers from `a` to `b`.
+gen :: Int -> Int -> [Int]
+gen a b | a > b     = [ b .. a ]
+        | otherwise = reverse [ a .. b ]