How to store an incomplete binary expression tree in an array?

Question

Data storage

How to store an incomplete binary expression tree in an array? If stored in the same way as the full one, then gaps (unused cells) appear in the array. In this case, you will still need to somehow mark these cells that they are not used. What do you suggest? It's about C++.

Answer 1

Auxiliary structures such as lsm-tree are used to store transactions.
I also advise you to look at how things are going with cache oblivious b-tree.