[英]unexpected behaviour in this program in python
我有这段代码可以根据给定的总和列表计算总和的最小硬币数量。 例如: minimum change for 69 with denomiations [25,10,5,1] : [25, 25, 10, 5, 1, 1, 1, 1]
: minimum change for 69 with denomiations [25,10,5,1] : [25, 25, 10, 5, 1, 1, 1, 1]
def get_min_coin_configuration(sum=None, coins=None, cache={}):
#if cache == None: # this is quite crucial if its in the definition its presistent ...
# cache = {}
if sum in cache:
return cache[sum]
elif sum in coins: # if sum in coins, nothing to do but return.
cache[sum] = [sum]
return cache[sum]
elif min(coins) > sum: # if the largest coin is greater then the sum, there's nothing we can do.
#cache[sum] = []
#return cache[sum]
return []
else: # check for each coin, keep track of the minimun configuration, then return it.
min_length = 0
min_configuration = []
for coin in coins:
results = get_min_coin_configuration(sum - coin, coins, cache)
if results != []:
if min_length == 0 or (1 + len(results)) < len(min_configuration):
#print "min config", min_configuration
min_configuration = [coin] + results
#print "min config", min_configuration
min_length = len(min_configuration)
cache[sum] = min_configuration
return cache[sum]
if __name__ == "__main__":
print "minimum change for 69 with denomiations [25,10,5,1] by recursive : ",get_min_coin_configuration(69,[25,10,5,1])
print "*"*45
print "minimum change for 7 with denomiations [4,3,1] by recursive : ",get_min_coin_configuration(7,[4,3,1])
当我注释掉主菜单中的任何一条打印语句时,该程序似乎运行良好。 当我同时调用两个函数时,它打印错误。 注释掉主体中的两个打印语句,您会看到它正确地打印了最少的硬币。
minimum change for 69 with denomiations [25,10,5,1] by recursive : [25, 25, 10, 5, 1, 1, 1, 1]
*********************************************
minimum change for 7 with denomiations [4,3,1] by recursive : [5, 1, 1]
if __name__ == "__main__":
cache_denom_set1 = {}
cache_denom_set2 = {}
print "minimum change for 69 with denomiations [25,10,5,1] by recursive : ",get_min_coin_configuration(69,[25,10,5,1],cache_denom_set1)
print "*"*45
print "minimum change for 7 with denomiations [4,3,1] by recursive : ",get_min_coin_configuration(7,[4,3,1],cache_denom_set2)
为每个面额传递单独的缓存
问题是您的缓存已经知道如何将7更改为5,1,1,因此它只返回...缓存不知道面额集中不再有5 ...
字典是可变的,如列表...这应该证明问题
def dict_fn(cache={}):
cache[len(cache.keys())] = 1
print cache
dict_fn()
dict_fn()
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