Weight-balanced tree
In computer science, weight-balanced binary trees (WBTs) are a type of self-balancing binary search trees that can be used to implement dynamic sets, dictionaries (maps) and sequences. These trees were introduced by Nievergelt and Reingold in the 1970s as trees of bounded balance, or BB[α] trees. Their more common name is due to Knuth.

Like other self-balancing trees, WBTs store bookkeeping information pertaining to balance in their nodes and perform rotations to restore balance when it is disturbed by insertion or deletion operations. Specifically, each node stores the size of the subtree rooted at the node, and the sizes of left and right subtrees are kept within some factor of each other. Unlike the balance information in AVL trees (which store the height of subtrees) and red–black trees (which store a fictional "color" bit), the bookkeeping information in a WBT is an actually useful property for applications: the number of elements in a tree is equal to the size of its root, and the size information is exactly the information needed to implement the operations of an order statistic tree, viz., getting the 'th largest element in a set or determining an element's index in sorted order.

Weight-balanced trees are popular in the functional programming community and are used to implement sets and maps in MIT Scheme, SLIB and implementations of Haskell.
Q21198
computer science
Concept
Q245955
self-balancing binary search tree
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Q1514741
dynamic set
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Q80585
dictionaries
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Q17457
Knuth
PER
Q541347
rotations
UNK
Q300159
AVL tree
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Q506496
red–black tree
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Q7100701
order statistic tree
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Q193076
functional programming
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Q768970
MIT Scheme
MEDIA
Q7390950
SLIB
ORG
Q34010
Haskell
MEDIA
Q7979855
Weight-balanced tree
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1970-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1970
DATE
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different from
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