Hi Kaoru,
I have been working through the exercises in Thompson's The Craft of Functional Programming 2nd Ed book. I am looking for a solution web site for Thompson's book. Or maybe the people here can help.
In exercise 4.4, I am asked to define a function
howManyOfFourEqual :: Int -> Int -> Int -> Int -> Int
which returns the number of integers that are equal to each other. For example,
howManyOfFourEqual 1 1 1 1 = 4 howManyOfFourEqual 1 2 3 1 = 2 howManyOfFourEqual 1 2 3 4 = 0
A solution which is applicable to any number of arguments is this: import Data.List howManyOfFourEqual a b c d = determineMaxEquals [a,b,c,d] determineMaxEquals :: [a] -> Int determineMaxEquals ls = head $ reverse $ sort $ map length $ group $ sort ls Of course, determineMaxEquals is fubar if used on an infinite list. Regards, Andy