states_needed = set(["mt", "wa", "or", "id", "nv", "ut", "ca", "az"])

stations = dict() stations["kone"] = set(["id", "nv", "ut"]) stations["ktwo"] = set(["wa", "id", "mt"]) stations["kthree"] = set(["or", "nv", "ca"]) stations["kfour"] = set(["nv", "ut"]) stations["kfive"] = set(["ca", "az"])

final_stations = set()

 while states_needed:
  # 遍历所有的广播台，从中选择覆盖最多的未覆盖州的广播台，将这个广播台存储在best_station中
  best_station = None
  # 这个集合包含该广播台覆盖的所有未覆盖的州
  states_covered = set()
  for station, states in stations.items():
   covered = states_needed & states
   if len(covered) > len(states_covered):
    best_station = station
    states_covered = covered
 states_needed -= states_covered
 final_stations.add(best_station)

print(final_stations) # 结果为{'ktwo', 'kthree', 'kone', 'kfive'}