Lowest Common Ancestor Algorithm

Question

So I have been looking into implementing a lowest common ancestor algorithm. I looked at many different algorithms (mainly variations of Trajan\'s solution or variations of the

Answer 1

Your algorithm is quadratic, but it can easily be made linear.

Just use hashtable (i.e. set) for parentNode, instead of list. Thus checking whether a node is in parentNode will be O(1) instead of O(n).