Data structure that allows accessing elements by index and delete them in O(1)

Question

I have following task (as part of bigger task):

I need to take an k element from array like data structure and delete it (k is any possible index). Arra

Answer 1

There is a solution, that may be satisfying in some cases. You have to use an array and a vector for saving deletions. Every time you delete an element, you put its index in a vector. Every time you read an element of some index, you recalculate its index depending on previous deletions.

Say, you have an array of:

A = [3, 7, 6, 4, 3]

You delete 3-rd element:

A = [3, 7, 6, 4, 3] (no actual deletion)
d = [3]

And then read the 4-th:

i = 4
3 < 4 => i += 1
A[i] = 3

This is not exactly O(1), but yet it does not depend on array length. Only on a number of deleted elements.