[英]Unknown issue with recursive integer partition calculator in Python
I'm having some trouble with my recursive program to calculate the number of integer partitions of an integer. 我的递归程序在计算整数的整数分区数时遇到了一些麻烦。
Here's what I have written: 这是我写的:
def p(k, n):
if k > n:
return 0
if k == 1:
return 1
else:
return (p(k+1, n) + p(k, n-k))
def partitions(n):
ans = 1
for k in range(1, n/2):
ans += p(k, n-k)
return ans
This algorithm is implemented from Wikipedia's article Partition (number theory) . 该算法是从Wikipedia的文章分区(数论)中实现的 。 Here's what my program outputs for the first few integers:
这是我的程序输出的前几个整数的内容:
partitions(0) = 1
partitions(1) = 1
partitions(2) = 1
partitions(3) = 1
partitions(4) = 2
partitions(5) = 2
partitions(6) = 2
partitions(7) = 2
I'm not sure why my program doesn't operate properly, since I thought I correctly implemented both recursion and the algorithm from Wikipedia. 我不确定为什么我的程序不能正常运行,因为我以为我正确地实现了Wikipedia的递归和算法。 Could somebody help me understand what it's doing?
有人可以帮助我了解它在做什么吗?
You have one of the base cases wrong: 您有一种错误的基本情况:
if k == 1:
return 1
should be 应该
if k == n:
return 1
Additionally: 另外:
for k in range(1, n / 2):
should be 应该
for k in range(1, n / 2 + 1):
This is because the sum in the formula is inclusive of the upper bound, but in Python, the range
does not include the upper bound. 这是因为公式中的总和包含上限,但在Python中,
range
不包含上限。 Then: 然后:
print [partitions(i) for i in range(1, 8)]
gives 给
[1, 2, 3, 5, 7, 11, 15]
matching the values given in the Wikipedia article . 匹配Wikipedia文章中给出的值。
I see two problems: 我看到两个问题:
This: 这个:
if k == 1:
should be if k == n:
, and this loop: 应该是
if k == n:
并且此循环:
for k in range(1, n/2):
should be range(1, n/2+1)
-- or better, range(1, n//2+1)
to be explicit about the fact we want integer division -- because range
in Python doesn't include the upper bound. 应该是
range(1, n/2+1)
-或更佳的是range(1, n//2+1)
可以明确表明我们想要整数除法的事实-因为Python中的range
不包括上位界。 After fixing those, I get: 修复这些问题后,我得到:
>>> [partitions(i) for i in range(1,10)]
[1, 2, 3, 5, 7, 11, 15, 22, 30]
(which, you'll notice, only has 9 values. :^) (您会注意到,它只有9个值。:^)
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