from binarytree import BinaryTreeNode
def is_bst(root: BinaryTreeNode) -> bool:
upper_bound = float('inf')
lower_bound = -float('inf')
return is_bst_helper(root, upper_bound, lower_bound)
def is_bst_helper(root: BinaryTreeNode, upper_bound: float, lower_bound: float) -> bool:
if root is None:
return True
if root.value > lower_bound and root.value < upper_bound:
return is_bst_helper(root.left, root.value, lower_bound) and is_bst_helper(root.right, upper_bound, root.value)
return False
bst = BinaryTreeNode(5)
bst.insert_left(4)
bst.insert_right(6)
bst.right.insert_right(7)
print(is_bst(bst))
badBst = BinaryTreeNode(7)
badBst.insert_left(6)
badBst.insert_right(15)
badBst.left.insert_right(8) # bad value -- bigger than root
print(is_bst(badBst))
def second_largest(root: BinaryTreeNode) -> BinaryTreeNode:
node = root
parent = root
while node.right is not None:
parent = node
node = node.right
if node.left is None:
return parent
else:
node = node.left
while node.right is not None:
node = node.right
return node
no_left_bst = BinaryTreeNode(5)
no_left_bst.insert_left(4)
no_left_bst.insert_right(6)
no_left_bst.right.insert_right(7)
print(second_largest(no_left_bst).value)
left_bst = BinaryTreeNode(5)
left_bst.left = BinaryTreeNode(3)
left_bst.right = BinaryTreeNode(8)
left_bst.right.left = BinaryTreeNode(7)
left_bst.right.right = BinaryTreeNode(12) #largest
left_bst.right.right.left = BinaryTreeNode(10) #left tree of largest
left_bst.right.right.left.left = BinaryTreeNode(9)
left_bst.right.right.left.right = BinaryTreeNode(11) #second largest
print(second_largest(left_bst).value)
