Rotation Distance, Triangulations and Hyperbolic Geometry
A rotation in a binary tree is a local restructuring that changes the tree into another tree. Rotations are useful in the design of tree-based data structures. The rotation distance between a pair of trees is the minimum number of rotations needed to convert one tree into the other. In this paper we establish
a tight bound of 2n - 6 on the maximum rotation distance between two n-node trees for all large n, using volumetric arguments in hyperbolic 3-space. Our proof also gives a tight bound on the minimum number of tetrahedra needed to dissect a polyhedron in the worst case, and reveals connections among binary trees, triangulations, polyhedra, and hyperbolic geometry.