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

Working on a red-black tree implementation I was getting problems validating the tree with multiple keys until I realized that with the red-black insert rotation, you have to loosen the constraint to

left <= root <= right

Since none of the documentation I was looking at allowed for duplicate keys and I didn't want to rewrite the rotation methods to account for it, I just decided to modify my nodes to allow for multiple values within the node, and no duplicate keys in the tree.