Cover trees
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The Cover Tree is a special type of data structure in computer science that is specifically designed to facilitate the speed-up of nearest neighbor searches. The tree can be thought of as a hierarchy of levels with the top level containing the root tuple and the bottom level containing every tuple in the metric space. Each level C is associated with an integer value i that decrements by one as the tree is descended. Each level C in the cover tree has three important properties:
Nesting: Covering: Separation: