An F# implementation of the lowest common ancestor problem. Provides 3 solutions:

• With a parent pointer - build paths from the root to the nodes and find the lowest node where these paths overlap.
• Without a parent pointer - build paths from the root using depth first search and then apply the first solution's algorithm
• Without a parent pointer - search using a pruning heuristic: once we have found one of the nodes in the tree we don't need to consider any nodes below it, as the LCA must be either it or a node above it.