I was going through the fundamentals of tree structure and the definition for ancestor is as follows:A node u is an ancestor of v if there is a path from u to v.Consider the node 11. Is node 2 (not the root, the other one on the left) an ancestor of node 11? It is strictly not a grandparent of 11, however, there does exist a path between these nodes. This is confusing to me, because this would also imply that the sibling nodes (5) of 11 would qualify as an ancestor.
Which all nodes will qualify as an ancestor?
terminology;data structures;trees
The root-2 is an ancestor of 11 (it's the great-grandparent) but you're asking about the 2 on the left, which is not an ancestor. There is no directed path from that node to 11 since the left-2 has no outgoing edges. Paths must respect the direction of the edges.  Siblings are not ancestors for the same reason.(Sometimes, we want to talk about a path that ignores the edge directions. These are usually referred to as something like paths in the underlying undirected graph.)