Add 2015 day 1

2015/day1.hs

@@ -0,0 +1,12 @@
+import Data.List
+
+day1steps :: [Char] -> [Int]
+day1steps xs = [if x == '(' then 1 else -1 | x <- xs]
+
+day1p1 :: [Char] -> Int
+day1p1 xs = sum(day1steps xs)
+
+day1p2 :: [Char] -> Maybe Int
+day1p2 xs = findIndex (== entrance) steps
+  where steps = scanl (\acc x -> acc + x) 0 (day1steps xs)
+        entrance = -1