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In computer science, a 2–3–4 tree (also called a 2–4 tree) is a self-balancing data structure that is commonly used to implement dictionaries. The numbers mean a tree where every node with children (internal node) has either two, three, or four child nodes: * a 2-node has one data element, and if internal has two child nodes; * a 3-node has two data elements, and if internal has three child nodes; * a 4-node has three data elements, and if internal has four child nodes. Image:2-3-4-tree-2-node.svg|2-node Image:2-3-4-tree-3-node.svg|3-node Image:2-3-4-tree-4-node.svg|4-node 2–3–4 trees are B-trees of order 4;〔. Section 6.2.4: Multiway Trees, pp. 481–491. Also, pp. 476–477 of section 6.2.3 (Balanced Trees) discusses 2-3 trees.〕 like B-trees in general, they can search, insert and delete in O(log ''n'') time. One property of a 2–3–4 tree is that all external nodes are at the same depth. 2–3–4 trees are an isometry of red–black trees, meaning that they are equivalent data structures. In other words, for every 2–3–4 tree, there exists at least one red–black tree with data elements in the same order. Moreover, insertion and deletion operations on 2–3–4 trees that cause node expansions, splits and merges are equivalent to the color-flipping and rotations in red–black trees. Introductions to red–black trees usually introduce 2–3–4 trees first, because they are conceptually simpler. 2–3–4 trees, however, can be difficult to implement in most programming languages because of the large number of special cases involved in operations on the tree. Red–black trees are simpler to implement, so tend to be used instead. == Properties == * Every node (leaf or internal) is a 2-node, 3-node or a 4-node, and holds one, two, or three data elements, respectively. * All leaves are at the same depth (the bottom level). * All data is kept in sorted order. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「2–3–4 tree」の詳細全文を読む スポンサード リンク
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