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