Pr\"{u}fer codes on vertex-colored rooted trees

TL;DR

This paper extends Pr"{u}fer codes to vertex-colored rooted trees, enabling encoding, comparison, and analysis of such trees without unique labeling, with applications to freight network decomposition.

Contribution

It introduces a canonical labeling method and a vertex-colored Pr"{u}fer code (VCPC) that captures isomorphism and subtree relations for vertex-colored rooted trees.

Findings

VCPC characterizes tree isomorphism.

VCPC encodes subtree relationships.

VCPC identifies minors of vertex-colored trees.

Abstract

Pr\"{u}fer codes provide an encoding scheme for representing a vertex-labeled tree on $n$ vertices with a string of length $n-2$. Indeed, two labeled trees are isomorphic if and only if their Pr\"{u}fer codes are identical, and this supplies a proof of Cayley's Theorem. Motivated by a graph decomposition of freight networks into a corpus of vertex-colored rooted trees, we extend the notion of Pr\"{u}fer codes to that setting, i.e., trees without a unique labeling, by defining a canonical label for a vertex-colored rooted tree and incorporating vertex colors into our variation of the Pr\"{u}fer code. Given a pair of trees, we prove properties of the vertex-colored Pr\"{u}fer code (abbreviated VCPC) equivalent to (1) isomorphism between a pair of vertex-colored rooted trees, (2) the subtree relationship between vertex-colored rooted trees, and (3) when one vertex-colored rooted tree is isomorphic to a minor of another vertex-colored rooted tree.