Let's assume the following definition of a red-black tree:
- It is a binary search tree.
- Each node is colored either red or black. The root is black.
- Two nodes connected by an edge cannot be red at the same time.
- Here should be a good definition of a NIL leaf, like on wiki. The NIL leaf is colored black.
- A path from the root to any NIL leaf contains the same number of black nodes.
Question
Suppose that you have implemented the insert
and delete
operations for the red-black tree. Now, if you are given a valid red-black tree, is there always a sequence of insert
and delete
operations that constructs it?
Motivation
This question is motivated by this question and by the discussion from this question.
Personally, I do believe that if you imagine a valid red-black tree consisting only of black nodes (which implies that you are imagining a perfectly balanced tree), there is a sequence of insert
and delete
operations that constructs it. However,
- I do not know how to accurately prove that
- I am also interested in the more general case
insert
anddelete
to construct a valid red-black tree consisting only of black nodes. It uses $(h + 2) \cdot 2^h - 1$ insertions/deletions to create a tree of height $h$. First, we can create a perfectly balanced red-black tree in breadth-first manner using $2^{h+1} - 1$ insertions, then using $h * 2^{h-1}$ insertions and the same amount of deletions repaint it into a completely black tree. The trick here is to move up $h$ times the lowest red layer up the tree until it reaches the root. $\endgroup$insert
anddelete
operations? $\endgroup$insert
anddelete
; there may be several ways to do these operations. b) Since RB trees are essentially B-trees of order 4, one can look there for inspiration. The details may prove tricky since the mapping from RB to B (and/or backwards) is not unique. $\endgroup$