すごいH本読書会 in 大阪 #1 練習問題

sugoih_osaka1.hs

-- ex1
-- my null
null' xs = xs == []

-- my sum
sum' xs = if null' xs then 0 else head xs + sum' (tail xs)

-- my product
product' xs = if null' xs then 1 else head xs * product' (tail xs)

-- my elem
elem' x xs = not (null' [y | y <- xs, x == y])

-- slice from python
slice n m xs = drop n (take m xs)

-- ex2
-- フィボナッチ数列のn番目を返す
fib n = if n == 1 then 1 else if n == 2 then 1 else fib (n - 1) + fib (n - 2)

-- FizzBuzzのn番目からm番目を返す
fizzBuzz n m = slice n m [if fizzBuzz n then "FizzBuzz" else if buzz n then "Buzz" else if fizz n then "Fizz" else show n | n <- [1..], let fizz x = x `mod` 3 == 0, let buzz y = y `mod` 5 == 0, let fizzBuzz z = fizz z && buzz z]

-- ex3
-- good integral numbers
goodIntegrals = take 4 [n | n <- [100..999], let split n = (read [h], read [t], read [o]) where (h:t:o:_) = show n, let (a,b,c) = split n, c /= 0, n `mod` (10 * a + b + c) == 0, n `mod` (10 * b + a + c) == 0]