Are duplicate keys allowed in the definition of binary search trees?

Question

I\'m trying to find the definition of a binary search tree and I keep finding different definitions everywhere.

Some say that for any given subtree the left child k

Answer 1

Any definition is valid. As long as you are consistent in your implementation (always put equal nodes to the right, always put them to the left, or never allow them) then you're fine. I think it is most common to not allow them, but it is still a BST if they are allowed and place either left or right.