greedy算法(python版)

greedy算法的核心思想是首先計算覆蓋面大的部分,而後依次尋找其餘覆蓋面最大的部分。該算法的使用場景就像他的名字同樣,當符合貪婪屬性的時候就能夠考慮。python

states_needed = set(['北京', '上海', '廣州', '深圳', '杭州', '南京', '石家莊', '銀川'])

stations = {}
stations['kone'] = set(['北京', '上海', '廣州'])
stations['ktwo'] = set(['北京''杭州', '南京'])
stations['kthree'] = set(['廣州', '深圳', '杭州'])
stations['kfour'] = set(['北京', '銀川'])
stations['kfive'] = set(['石家莊', '銀川'])

final_stations = set()

while states_needed:
    best_station = None
    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)
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