算法——贪婪算法

贪婪算法：每步都采取最优的做法，最终得到的就是全局最优解

"""
贪婪算法
覆盖所有的州，最小集合
方法：
（1）选出一个广播，它覆盖了最多的未覆盖州，即便广播台覆盖了一些已经覆盖的州，也没有关系
（2）重复第一步，知道所有的州都被覆盖
"""

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

stations = {
    'kone': set(['id', 'nv', 'ut']),  # kone 覆盖这些州
    'ktwo': set(['wa', 'id', 'mt']),
    'kthree': set(['or', 'nv', 'ca']),
    'kfour': set(['nv', 'ut']),
    'kfive': set(['ca', 'az'])
}
best_result = []
final_states = set()
while states_needed:
    best_station = None
    best_states = set()
    for station, states in stations.items():
        covered = states_needed & states
        if len(covered) > len(best_states):
            best_station = station
            best_states = covered
    best_result.append(best_station)
    states_needed -= best_states
    final_states |= best_states

    
print(best_result)  # ['kone', 'ktwo', 'kthree', 'kfive']