V
 the graph vertex typeE
 the graph edge typepublic class NaiveLcaFinder<V,E> extends Object
Find the LCA, defined as Let G = (V, E) be a DAG, and let x, y ∈ V . Let G x,y be the subgraph of G induced by the set of all common ancestors of x and y. Define SLCA (x, y) to be the set of outdegree 0 nodes (leafs) in G x,y . The lowest common ancestors of x and y are the elements of SLCA (x, y). This naive algorithm simply starts at a and b, recursing upwards to the root(s) of the DAG. Wherever the recursion paths cross we have found our LCA. from http://www.cs.sunysb.edu/~bender/pub/JALG05daglca.pdf. The algorithm:
1. Start at each of nodes you wish to find the lca for (a and b) 2. Create sets aSet containing a, and bSet containing b 3. If either set intersects with the union of the other sets previous values (i.e. the set of notes visited) then that intersection is LCA. if there are multiple intersections then the earliest one added is the LCA. 4. Repeat from step 3, with aSet now the parents of everything in aSet, and bSet the parents of everything in bSet 5. If there are no more parents to descend to then there is no LCAThe rationale for this working is that in each iteration of the loop we are considering all the ancestors of a that have a path of length n back to a, where n is the depth of the recursion. The same is true of b.
We start by checking if a == b.
if not we look to see if there is any intersection between parents(a) and (parents(b) union b)
(and the same with a and b swapped)
if not we look to see if there is any intersection between parents(parents(a)) and
(parents(parents(b)) union parents(b) union b) (and the same with a and b swapped)
continues
This means at the end of recursion n, we know if there is an LCA that has a path of <=n to a and b. Of course we may have to wait longer if the path to a is of length n, but the path to b>n. at the first loop we have a path of 0 length from the nodes we are considering as LCA to their respective children which we wish to find the LCA for.
Constructor and Description 

NaiveLcaFinder(DirectedGraph<V,E> graph)
Create a new instance of the native LCA finder.

public NaiveLcaFinder(DirectedGraph<V,E> graph)
graph
 the input graphCopyright © 2016. All rights reserved.