Algorithm to find lowest common ancestor in directed acyclic graph?

Question

Imagine a directed acyclic graph as follows, where:

• \"A\" is the root (there is always exactly one root)
• each node knows its parent(s)
• the no

Answer 1

This link (Archived version) describes how it is done in Mercurial - the basic idea is to find all parents for the specified nodes, group them per distance from the root, then do a search on those groups.