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Vel Tech exam 2018 P22600

Statement

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Write a function df :: Int -> Int that returns the double factorial of a natural number. The double factorial of n is denoted n!! and is n(n−2)(n−4)….
Write a function sumd :: Int -> Int that returns the sum of the digits of a natural number.
Write a function dup :: [Int] -> [Int] that duplicates each element in a list.
Write a function pal :: String -> Bool that tells if a string is a palindrome, ie, if it is equal to its reverse.
Write a function apply2 :: (a -> a) -> a -> a that applies a function twice to some parameter.

Public test cases

Input

df 0
df 1
df 2
df 3
df 10
df 11
df 13

Output

Input

sumd 0
sumd 3
sumd 23
sumd 999
sumd 8756

Output

Input

dup [1,2,3]
dup []
dup [666]
dup [4,4,2,3,8,2]

Output

[1,1,2,2,3,3]
[]
[666,666]
[4,4,4,4,2,2,3,3,8,8,2,2]

Input

pal "abcba"
pal "xyzaz"
pal ""
pal "a"
pal "aa"
pal "aba"
pal "abb"
pal "abcdedcbz"

Output

True
False
True
True
True
True
False
False

Input

apply2 (+ 2.5) 10.5
apply2 (* 3) 4
apply2 ("hello " ++) "peter"

Output

15.5
36
"hello hello peter"

Information