Editing Red–black tree (section)

== Terminology ==

The '''black depth''' of a node is defined as the number of black nodes from the root to that node (i.e. the number of black ancestors). The '''black height''' of a red–black tree is the number of black nodes in any path from the root to the leaves, which, by [[#req4|requirement 4]], is constant (alternatively, it could be defined as the black depth of any leaf node).<ref name="Mehlhorn2008">{{cite book
|chapter=7. Sorted Sequences
|chapter-url=http://people.mpi-inf.mpg.de/~mehlhorn/ftp/Toolbox/SortedSequences.pdf
|title=Algorithms and Data Structures: The Basic Toolbox
|url=http://people.mpi-inf.mpg.de/~mehlhorn/Toolbox.html
|last1=Mehlhorn |first1=Kurt |author-link1=Kurt Mehlhorn
|last2=Sanders|first2=Peter |author-link2=Peter Sanders (computer scientist)
|publisher=Springer |location= Berlin/Heidelberg
|year=2008
|isbn=978-3-540-77977-3
|doi=10.1007/978-3-540-77978-0 |citeseerx=10.1.1.148.2305
}}</ref>{{rp|154–165}}
The black height of a node is the black height of the subtree rooted by it. In this article, the black height of a null node shall be set to 0, because its subtree is empty as suggested by the example figure, and its tree height is also 0.