递归地将列表递减 1 [英] Recursively decrement a list by 1

问题描述

非常快速和简单的家庭作业问题.我运行正常，但我认为有更好的
方法来做到这一点.一种更 Pythonic 的方式.
这是我的代码，以递归方式将列表的每个元素递减 1.

Very quick and easy homework question. I have it running ok but I think there's a better
way to do it. A more Pythonic way.
Here's my code to recursively decrement each element of a list by 1.

l = range(30)  
def recurseDecrMap(l, x = []):  
    if len(l) == 0:  
        return []  
    else:  
        x.append(l[0] -1)  
    recurseDecrMap(l[1:], x)  
    return x  

所以感谢您的任何意见.我正在努力学习做更好的递归.获取困难
它的诀窍.

So thanks for any input. I'm trying to learn to do better recursion. Having trouble getting
the knack of it.

推荐答案

你只能使用一个参数，在我看来它更简单:

You can use only one argument, in my opinion it is simpler:

def recurseDecrMap(l):  
    if not l:  
        return []  
    else:
        return [l[0]-1] + recurseDecrMap(l[1:])

但正如@jamylak 指出的那样，这个算法的复杂度是 O(N^2)，因为 l[1:] 创建了一个新列表，其中引用了列表.

But as @jamylak pointed out, the complexity of this algorithm is O(N^2), since l[1:] creates a new list with references to the rest of the items in the list.

如果您需要效率，我建议您使用列表推导式 (Haidro 的回答)，但我认为如果您仅出于学习目的而想要它，这不是优先事项.

If you need efficiency, I'd recommend you using list comprehensions (Haidro's answer), but I suppose it is not a priority if you want it only for learning purposes.

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