I have some strings as input and I need to manipulate their individual characters, which I do more efficiently by first splitting the strings into arrays of characters. So in short, my algorithm is duplicating the input. What would be its space complexity?
The same space complexity as the original problem.
If you have an input of n characters arranged in strings, that carries a spatial complexity of O(n). All you do is arrange them in some different way and duplicating the space you need: 2n and thus having a complexity of O(2n).
However O(n) is equivalent to O(kn), being k any constant. Doesn't mean both problems consume the same memory but complexity wise they are equivalent.