为什么我们必须定义变量 dp = [0] * (n+1) 只是为了将其变量设置为等于 0（在动态规划中）

Question

我有一些关于某人定义的问题： dp = [0] * (n + 1)只是为了将变量设置为 0，它想做什么？

Answer 1

In Python you can multiply a list and tuple with an integer n . It will then generate a list or tuple with a length l×n with l the length of the given list/tuple. It will repeat the elements in that collection, like:

>>> [1,4,2,5]*3
[1, 4, 2, 5, 1, 4, 2, 5, 1, 4, 2, 5]
>>> (1,4,2,5)*3
(1, 4, 2, 5, 1, 4, 2, 5, 1, 4, 2, 5)

Since here the given list is a singleton, you thus construct a list with length n+1 where each element is 0 , like:

>>> [0] * (5 + 1)
[0, 0, 0, 0, 0, 0]

When you multiply a list/tuple with an integer, the references of the items are coped. You thus do not make a "deep copy" of the values. Since int s are immutable, that does not matter. But if the elements are lists for example, you did not make copies of that list, you made a list where you referenced the same list multiple times.