文章目录
Validating Credit Card Numbers
doubleList :: [Integer] -> [Integer]
doubleList [] = []
doubleList (x:[]) = [x]
doubleList (x:(y:zs)) = (2*x):y:doubleList zs
addDigits :: [Integer] -> Integer
addDigits [] = 0
addDigits (x:zs) = getDigits x+addDigits zs
getDigits :: Integer -> Integer
getDigits n
| n < 0 = 0
| n < 10 = n
| otherwise = mod n 10 + getDigits (div n 10)
isValid :: Integer -> Bool
isValid n = (mod n 10)==0
main = do
print(doubleList [1,3,8,6])
print(addDigits [2,3,16,6])
print(isValid 18)
Exercise 1
toDigits :: Integer -> [Integer]
toDigitsRev :: Integer -> [Integer]
toDigits n
| n < 10 && n > 0 = [n]
| n >= 10 = toDigits (div n 10) ++ (mod n 10 : [])
| otherwise = []
toDigitsRev n
| n < 10 && n > 0 = [n]
| n >= 10 = mod n 10 : toDigitsRev (div n 10)
| otherwise = []
main = do
print(toDigits 1234)
print(toDigitsRev 1234)
Exercise 2
doubleList :: [Integer] -> [Integer]
doubleList [] = []
doubleList (x:[]) = [x]
doubleList (x:(y:zs)) = (x):(2*y):doubleList zs
doubleEveryOther :: [Integer] -> [Integer]
doubleEveryOther n
= reverse (doubleList (reverse n))
main = do
print(doubleEveryOther [8,7,6,5])
Exercise 3
sumDigits :: [Integer] -> Integer
sumDigits [] = 0
sumDigits (x:zs) = getDigits x+sumDigits zs
getDigits :: Integer -> Integer
getDigits n
| n < 0 = 0
| n < 10 = n
| otherwise = mod n 10 + getDigits (div n 10)
main = do
print(sumDigits [16,7,12,5])
Exercise 4
sumDigits :: [Integer] -> Integer
sumDigits [] = 0
sumDigits (x:zs) = getDigits x+sumDigits zs
getDigits :: Integer -> Integer
getDigits n
| n <= 0 = 0
| n < 10 = n
| otherwise = mod n 10 + getDigits (div n 10)
isValid :: Integer -> Bool
isValid n = (mod (getDigits n) 10)==0
main = do
print(isValid 4012888888881881)
Exercise 5
简单的汉诺塔问题
type Peg = String
type Move = (Peg,Peg)
hanoi :: Integer -> Peg -> Peg -> Peg -> [Move]
hanoi n a b c
| n==1 = [(a,b)]
| otherwise = (getHanoiMiddleResult (n-1) a b c) ++ [(a,b)] ++ (getHanoiMiddleResult (n-1) c a b)
getHanoiMiddleResult :: Integer -> Peg -> Peg -> Peg -> [Move]
getHanoiMiddleResult n a b c
|n>1 = (a,c) : getHanoiMiddleResult (n-1) a b c
|otherwise = [(a,c)]
main = do
print(hanoi 2 "a" "b" "c")
