Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

Figure 10.26: Red-black tree associated with the (2,4)
tree of Figure 10.20. Each external node of this red-black
tree has 4 black ancestors (including itself); hence, it has
black depth 3. We use the color blue instead of red. Also,
we use the convention of giving an edge of the tree the
same color as the child node.
As for previous types of search trees, we assume that entries are stored at the internal
nodes of a red-black tree, with the external nodes being empty placeholders. Also, we
assume that the external nodes are actual nodes, but we note that, at the expense of
slightly more complicated methods, external nodes could be null.
We can make the red-black tree definition more intuitive by noting an interesting
correspondence between red-black trees and (2,4) trees, as illustrated in Figure 10.27.
Namely, given a red-black tree, we can construct a corresponding (2,4) tree by
merging every red node v into its parent and storing the entry from v at its parent.
Conversely, we can transform any (2,4) tree into a corresponding red-black tree by
coloring each node black and performing the following transformation for each
internal node v:
• If v is a 2-node, then keep the (black) children of v as is.
• If v is a 3-node, then create a new red node w, give v's first two (black) children to
w, and make w and v's third child be the two children of v.
• If v is a 4-node, then create two new red nodes w and z, give v's first two (black)
children to w, give v's last two (black) children to z, and make w and z be the two
children of v.
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