##### Wikipedia

**BK-tree**

A **BK-tree** is a metric tree suggested by Walter Austin Burkhard and Robert M. Keller specifically adapted to discrete metric spaces. For simplicity, let us consider **integer** discrete metric *d*(*x*, *y*). Then, BK-tree is defined in the following way. An arbitrary element *a* is selected as root node. The root node may have zero or more subtrees. The *k-th* subtree is recursively built of all elements *b* such that *d*(*a*, *b*) = *k*. BK-trees can be used for approximate string matching in a dictionary .