Root-Balanced Tree

Andersson [1, 2] introduced general balanced trees, search trees based on the design principle of partial rebuilding: perform update operations naively until the tree becomes too unbalanced, at which point a whole subtree is rebalanced. This article defines and analyzes a functional version of general balanced trees, which we call root-balanced trees. Using a lightweight model of execution time, amortized logarithmic complexity is verified in the theorem prover Isabelle. This is the Isabelle formalization of the material decribed in the APLAS 2017 article Verified Root-Balanced Trees by the same author [3] which also presents experimental results that show competitiveness of root-balanced with AVL and red-black trees.