8-20、贪婪算法

贪婪算法：

每步都采取最优的做法，你每步都选择局部最优解，最终得到的就是全局最优解。

##创建一个列表，其中包含要覆盖的州
states_needed = set(["mt", "wa", "or", "id", "nv", "ut", "ca", "az"])
stations = {}
stations["kone"]   = set(["id", "nv", "ut"])
stations["ktwo"]   = set(["wa", "id", "mt"])
stations["kthres"] = set(["or", "nv", "ca"])
stations["kfour"]  = set(["nv", "ut"])
stations["kfive"]  = set(["ca", "az"])

#使用一个集合来存储最终选择的广播台
final_stations     = set()

while states_needed:
    best_station   = None
    states_covered = set()
    for station, states_for_station in stations.items():
        covered = states_needed & states_for_station
        if len(covered) > len(states_covered):
            best_station   = station
            states_covered = covered
    states_needed -= states_covered
    final_stations.add(best_station)
	
print(final_stations)