A post claims 5 of the trees shown in the following figure are all binary search trees
I guess the author's making a mistake, since the 2 trees on the right ARE NOT binary search trees.
As an example, in the last tree pointed out by red rectangle, the key
1 is in
2's right subtree, which doesn't satisfy the binary-search-tree property.
Besides the figure above, the post also says
the BST is an ordered data structure that allows no duplicate values
which, I guess, is another mistake.
Correcting the bugs above, I'd like to make the following conclusion,
all the keys in a binary search tree should be greater than or equal to the root of the tree,
or more precisely, in a binary search tree, all the keys of a subtree should be greater than or equal to the root of the subtree,
is my understanding correct?
one of my references: