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Pattern avoidance in ternary trees
Journal of Integer Sequences (2012)
  • Nathan Gabriel, Rice University
  • Katie Peske
  • Lara K. Pudwell, Valparaiso University
  • Sam Tay, Kenyon College

This paper considers the enumeration of ternary trees (i.e., rooted ordered trees in which each vertex has 0 or 3 children) avoiding a contiguous ternary tree pattern. We begin by finding recurrence relations for several simple tree patterns; then, for more complex trees, we compute generating functions by extending a known algorithm for pattern-avoiding binary trees. Next, we present an alternate one-dimensional notation for trees which we use to find bijections that explain why certain pairs of tree patterns yield the same avoidance generating function. Finally, we compare our bijections to known “replacement rules” for binary trees and generalize these bijections to a larger class of trees.

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Citation Information
Nathan Gabriel, Katie Peske, Lara K. Pudwell and Sam Tay. "Pattern avoidance in ternary trees" Journal of Integer Sequences Vol. 15 Iss. 12.5.1 (2012)
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