如何将元素插入列表中的任意位置? [英] How to insert elements into the list at arbitrary positions?

问题描述

我有这个

>>> a = [1, 4, 7, 11, 17]

有没有办法在其他元素之间随机添加4个字符'-'，例如

Is there any way to add 4 characters '-' randomly between the other elements to achieve, for example

['-', 1, '-', 4, 7, '-', '-', 11, 17]

推荐答案

您可以轻松地做到:

import random
for _ in range(4):
    a.insert(random.randint(0, len(a)), '-')

循环主体在 0 和 len(a)(含)之间的随机索引处插入'-'.但是，由于插入到列表中的代码是 O(N)，因此根据插入的数量和列表的长度，最好在性能上构造一个新列表:

The loop body inserts a '-' at a random index between 0 and len(a)(inclusive). However, since inserting into a list is O(N), you might be better off performance-wise constructing a new list depending on the number of inserts and the length of the list:

it = iter(a)
indeces = list(range(len(a) + 4))
dash_indeces = set(random.sample(indeces, 4))  # four random indeces from the available slots
a = ['-' if i in dash_indeces else next(it) for i in indeces]

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