hotel-ranking.hs

data HotelRank = HotelRank { idh :: Integer, rank :: Integer } deriving (Show, Eq)                                                     

instance Ord HotelRank where
  compare (HotelRank i r) (HotelRank i' r')                                                                                            
    | r == r' = compare i i'                                                                                                           
    | otherwise = if compare r r' == GT then LT else GT
                                                                                                                                       
l = [(4000, 8), (3000, 7), (2000, 8), (1000, 5), (2000, 5), (4000, 5), (3000, 2)]                                                      
                                                                                                                                       
rankings = map (\(i, r) -> (HotelRank i r)) l                                                                                          
                                                                                                                                       
rankingsMap = foldl fn M.empty rankings
  where fn acc h = case M.lookup (idh h) acc of
                    Just(h') -> M.insert (idh h) (h' { rank = rank h + rank h' }) acc
                    _ -> M.insert (idh h) h acc

mergedRankings = M.elems rankingsMap
                                                                                                                                       
sortedRangkings = L.sort mergedRanking