Let’s say there are two persons, Composer and Performer.

The Composer randomly selects three different Pitch which constructed by two part, Note and Octave. Note in the range of “A” to “G”, Octave in the range of “1” to “3”.

For example, here is a typical Pitch combined by ‘A’ and ‘1’, in which ‘A’ is the Note, and ‘1’ is the Octave.

Once Composer selected a Combination, Performer needs to guess it as quick as possible. After each guess, Performer get a feedback which indicates that:

  • how many pitches in the guess are included in the target (correct pitches)
  • how many pitches have the right note but the wrong octave (correct notes)
  • how many pitches have the right octave but the wrong note (correct octaves)

Now, the question is how to get the corrected answer as less times as possible.

Haskell moment

Here are some Haskell code chunks, which both are simple recursion algorithms.

Quicksort is a sort of poster child for Haskell because everyone does it to showcase how elegant Haskell is.

quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) =
let smallerSorted = quicksort [a | a <- xs, a <= x]
    biggerSoted = quicksort [a | a <- xs, a > x]
in smallerSorted ++ [x] ++ biggerSoted
maximum' :: (Ord a) => [a] -> a
maximum' [] = error "List is empty!"
maximum' [x] = x
maximum' (x:xs) = (max x (maximum' xs))

replicate' :: Int  -> b -> [b]
replicate' n x
    | n <= 0 = []
    | otherwise = (x:(replicate' (n-1) x))

take' :: Int -> [a] -> [a]
take' n (x:xs)
    | n <= 0 = []
    | otherwise = x:(take' (n-1) xs)

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