TrueLogic 仕事日記

第３章の練習問題(P72)をやってみた．

1.リストの長さ

myLength :: [a] -> Int
myLength [] = 0
myLength (x:xs) = 1 + myLength xs

2. そのテストプログラム

testLength :: [a] -> String
testLength l
  | length l == myLength l = "OK"
  | otherwise = "NG"
                
-- testLength []
-- testLength [1,2,3,4,5]

3.リストの平均値

sumList :: [Double] -> Double                
sumList [] = 0
sumList (x:xs) = x + sumList xs

aveList :: [Double] ->  Double
aveList a = (sumList a) / fromIntegral (myLength a)

-- aveList [3,4]

4. 回文をつくる

myKaibun :: [a] -> [a]
myKaibun  = 
myKaibun (x:xs) = [x] ++ (myKaibun xs) ++ [x]

5. 回文の判定

myKaibunHantei :: [Char] -> String
myKaibunHantei [] = "OK"
myKaibunHantei (x:[]) = "OK"
myKaibunHantei (x:xs) =
    if x == (last xs)
    then myKaibunHantei (init xs)
    else "NG"