A 2-3 Tree is a specific form of a B tree. A 2-3 tree is a search tree. However, it is very different from a binary search tree.
Here are the properties of a 2-3 tree:
- each node has either one value or two value
- a node with one value is either a leaf node or has exactly two children (non-null). Values in left subtree < value in node < values in right subtree
- a node with two values is either a leaf node or has exactly three children (non-null). Values in left subtree < first value in node < values in middle subtree < second value in node < value in right subtree.
- all leaf nodes are at the same level of the tree
The insertion algorithm into a two-three tree is quite different from the insertion algorithm into a binary search tree. In a two-three tree, the algorithm will be as follows:
- If the tree is empty, create a node and put value into the node
- Otherwise find the leaf node where the value belongs.
- If the leaf node has only one value, put the new value into the node
- If the leaf node has more than two values, split the node and promote the median of the three values to parent.
- If the parent then has three values, continue to split and promote, forming a new root node if necessary