W2L1(Lecture3)-FP24-Vlad-Batch2Q5-WL

import Data.List

reindex :: (Int -> Int) -> [a] -> [a]
reindex f xs = map fst (sortBy sortFunction elements_indexes_after_f)
  where
    elements_indexes = zip xs [0 .. length xs - 1]
    elements_indexes_after_f = map (\(x, id) -> (x, f id)) elements_indexes
    sortFunction x y
      | snd x < snd y = LT
      | snd x > snd y = GT
      | otherwise = EQ
    -- (Shorter) alternative: sortFunction = \(_, a)  (_, b) -> compare a b