2015 Day 17 in Haskell

2015/day17/day17.hs

@@ -0,0 +1,34 @@
+import Aoc
+
+numWays :: Int -> [Int] -> Int
+numWays 0 _ = 1
+numWays _ [] = 0
+numWays n (x:xs)
+    | n > 0 = numWays (n-x) xs + numWays n xs
+    | otherwise = 0
+
+part1 :: [Int] -> Int
+part1 = numWays 150
+
+numWays' :: Int -> [Int] -> (Int, Int)
+numWays' 0 _ = (0, 1)
+numWays' _ [] = (0, 0)
+numWays' n (x:xs)
+    | n < 0 = (0, 0)
+    | w1 == 0 = (m0 + 1, w0)
+    | w0 == 0 = (m1, w1)
+    | m0 > m1 -1  = (m1, w1)
+    | m0 == m1 - 1 = (m1, w0 + w1)
+    | m0 < m1 -1 = (m0 + 1, w0)
+    | otherwise = undefined
+    where
+        (m0, w0) = numWays' (n-x) xs
+        (m1, w1) = numWays' n xs
+
+-- numWays and numWays' can be combined, but I think that that will make it too messy
+
+part2 :: [Int] -> Int
+part2 = snd . numWays' 150
+
+main :: IO ()
+main = aocMain (map read) part1 part2