Question

This is a follow up to
Is a list implementation of binary tree scalable?

What can be the advantages or disadvantages of tree implementation done
using linear array(stl vector) or stl deque

rather than a binary tree with individual nodes having left and right pointers?

assumptions:
the tree will be precomputed and will not be modified once built, and will only be used for searching.

Answer 1

Well, I’d say it’s something of these:

• with a pointer-tree, you use memory for data and pointers to data, while with std::vector you only allocate memory for the data (the container deals with iterating through itself)
• if you use std::vector, you memory is localized. E.g. if you want to access a single full level of a tree, that will be sequential in memory, while with individual nodes allocated separately, you would jump through the memory like a bunny rabbit accessing all that
• if you allocate individual nodes, you actually have no way to allocate them except individually. That means a lot of calls to the malloc-euqivalent function. (There are some tricks you could use to avoid that in C, and they still work in C++, but why go with hacks if you have a ready std::vector solution).
• when creating a vector, you can use std::vector.reserve() to preallocate all the memory. Additionally, if you know how vector operates, you know that it will call a malloc-equivalent for reserving memory approximately every time you start a new level of your tree – number of allocations should be roughly equal to number of levels in your tree
• accessing elements of a vector is so easy, navigating through a vector-based fully populated binary tree is very intuitive and easy to work with