Add 2015 day 9

haskellAoC/src/Y2015/Day09.hs

@@ -1,14 +1,35 @@
 module Y2015.Day09 (y15day09) where
 
+import qualified Data.Map as M
+
+import Data.List
 import Data.List.Split
 
 parseInput :: String -> (String, String, Int)
-parseInput input = (city1, city2, dist)
+parseInput input = parseInput' $ splitOn " " input
-  where (city1:split1:_) = splitOn " to " input
+  where parseInput' [c1, "to", c2, "=", d] = (c1, c2, read d)
-        (city2:raw_dist:_) = splitOn " = " split1
+
-        dist = read $ raw_dist
+getCities :: [(String, String, Int)] -> [String]
+getCities input = nub $ cities
+  where cities = getCities' input
+        getCities' [] = []
+        getCities' ((c1, c2, _):next) = c1:c2:(getCities' next)
+
+distanceToTuples :: (String, String, Int) -> [((String, String), Int)]
+distanceToTuples (c1, c2, d) = [((c1, c2), d), ((c2, c1), d)]
+
+computeTotalDistance :: M.Map (String, String) Int -> [String] -> Int
+computeTotalDistance dists (c1:c2:next) = (dists M.! (c1, c2)) + computeTotalDistance dists (c2:next)
+computeTotalDistance _ _ = 0
+
+-- A bit naive implementation, but the low volume of cities (permutations) make it doable
 
 y15day09 :: [String] -> (String, String)
 y15day09 input = (part1, part2)
-  where part1 = show $ map parseInput input
+  where part1 = show $ minimum $ allDistances
-        part2 = "WIP"
+        part2 = show $ maximum $ allDistances
+        distances = map parseInput input
+        cities = getCities distances
+        distancesMap = M.fromList $ concatMap distanceToTuples distances
+        allPermutations = permutations $ cities
+        allDistances = map (computeTotalDistance distancesMap) $ allPermutations