[英]Python Subset Sum Problem for Given Length of Elements
对于给定的集合,元素的总和和长度,
我想获取布尔值是否满足条件
例如...
Input : set = [18,0,2,20], sum = 20, length = 2 <br>
Output : True (subset [18,2] satisfy the sum=20 for given length 2)
Input : set = [18,0,2,20], sum = 22, length = 1 <br>
Output : False
如果存在给定的长度限制,我该如何解决该问题?
(如果没有长度条件,我可以轻松解决它: subset-sum-problem )
def isSubsetSum(set, n, sum):
if sum == 0:
return True
if (sum != 0) and (n == 0):
return False
if (set[n-1] > sum):
return isSubsetSum(set,n-1,sum)
# (a) including the last element
# (b) excluding the last element
# Not "AND", But "OR" !!!!!
return isSubsetSum(set,n-1,sum) or isSubsetSum(set,n-1,sum-set[n-1])
如果允许使用导入的模块,则itertools具有组合功能,可以使此操作非常容易:
from itertools import combinations
set = [18,0,2,20]
total = 20
length = 2
result = [ c for c in combinations(set,length) if sum(c) == total ]
if result:
print("True, subset ",result[0],"satisfies the sum", total, "given length",length)
else:
print("False")
如果需要将其用作递归函数,请考虑对于集合中的每个元素X
,如果可以在总计sum-X
的后续元素中找到N-1
元素的子集,则有sum/length=N
例如:
def subSum(numbers,total,length):
if len(numbers) < length or length < 1:
return []
for index,number in enumerate(numbers):
if length == 1 and number == total:
return [number]
subset = subSum(numbers[index+1:],total-number,length-1)
if subset:
return [number] + subset
return []
使用itertools.combinations
:
from itertools import combinations
inp = [18,0,2,20]
length = 2
sum_ = 20
def isSubsetSum(data, length, sum_):
data = [i[0]+i[1] for i in combinations(data,length)]
if sum_ in data:
return True
return False
print(isSubsetSum(inp,length, sum_))
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