Python实现的贪婪算法

# 使用Python实现贪婪算法
# 集合覆盖问题 
# 假设你办了个广播节目，要让全美50个州的听众都收听到。为此，你需要决定在哪些广播台播出。在每个广播台播出都需要支出费用，因此你力图在尽可能少的广播台播出  
# 1.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"])
# 2.使用散列表表示可供选择的广播台清单
 stations = dict() stations["kone"] = set(["id","ut"]) stations["ktwo"] = set(["wa","mt"]) stations["kthree"] = set(["or","ca"]) stations["kfour"] = set(["nv","ut"]) stations["kfive"] = set(["ca","az"])
# 3.使用集合来存储最终选择的广播台
 final_stations = set()
# 5.循环
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‘}