問題「隔離された街のゲート」 | エンジニアが死滅シタ世界 〜アンドロイドとふたりぼっちで生きろ〜

gate.hs

decode :: String -> [Int]
decode "U" = [ 0,  1]
decode "D" = [ 0, -1]
decode "L" = [-1,  0]
decode "R" = [ 1,  0]
decode _   = [ 0,  0]

(.+) :: Num a => [a] -> [a] -> [a]
(.+)  = zipWith (+)

f :: String -> String
f input = show $ 
    let
        [h, w] = take 2 . fmap read . words . head . lines $ input
        positions = scanl (.+) [0,0] . fmap decode . tail . lines $ input
        validate [x, y] = x >= 0 && y >= 0 && x < w && y < h
        validate _ = False
    in all validate positions
    where 
        show True = "valid"
        show False = "invalid"

main :: IO ()
main = interact f

testStr1 = "3 3 5\nU\nR\nD\nR\nL\n"

testStr2 = "4 4 7\nU\nU\nR\nR\nR\nR\nD\n"