code: def frequent_antennas(positions, percentage=0.8):
      
      location_count = Counter(list(map(str, positions)))
  
      target = math.ceil(sum(location_count.values()) * percentage)
      location_sort = sorted(list(location_count.keys()),
                             key=lambda x: location_count[x])
  
      while target > 0 and len(location_sort) > 0:
          location_id = location_sort.pop()
          target -= location_count[location_id]
  
      return len(location_count) - len(location_sort)
docs: The number of location that account for 80% of the locations where the user was.
      Percentage can be supplied as a decimal (e.g., .8 for default 80%).