func_code: def swap_unique_keys_values(d):
      e = {}
      h = {}
      for k, v in sorted(list(d.items()), reverse=True):
          if v not in e:
              e[v] = k
          else:
              e[v] = 'n'
      for k, v in sorted(list(e.items()), reverse=True):
          if v != 'n':
              h[k] = v
      return h