func_code: def swap_unique_keys_values(d):
      a2 = {}
      a3 = {}
      ar = sorted(list(d.items()), reverse=True)
      for k, v in ar:
          if v not in a2:
              a2[v] = k
          else:
              a2[v] = 'N'
      ar2 = sorted(list(a2.items()), reverse=True)
      for k, v in ar2:
          if v != 'N':
              a3[k] = v
      return a3