Lowest Common Ancestor with Linking Roots (Lowest Common Ancestor)

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Given a collection of rooted trees, answer queries of the form, "What is the nearest common ancestor of vertices $x$ and $y$?" In this version of the problem, The queries are given on-line. Interspersed with the queries are on-line commands of the form $link(x, y)$ where $x$ and $y$ are tree roots. The effect of a command $link(x, y)$ is to combine the trees containing $x$ and $y$ by making $x$ the parent of $y$.

Related Problems

Generalizations: Lowest Common Ancestor

Related: Off-Line Lowest Common Ancestor, Lowest Common Ancestor with Static Trees, Lowest Common Ancestor with Linking, Lowest Common Ancestors with Linking and Cutting


$n$: number of vertices

$m$: number of total number of operations (queries, links, and cuts)

Table of Algorithms

Name Year Time Space Approximation Factor Model Reference
Modified van Leeuwen (Linking Roots) 1976 $O(n+m*log(log(n)$)) $O(n)$ Exact Deterministic Space
Harel, Tarjan (Linking Roots) 1984 $O(n+ m*alpha(m + n, n)$) where alpha is the inverse Ackermann function $O(n)$ Exact Deterministic Time & Space