def constructTree(preorderArray):
stack = []
root = BST.BinaryTreeNode(preorderArray[0])
stack.append(root)
for value in preorderArray[1:]:
if value < stack[-1].data:
new_left_node = BST.BinaryTreeNode(value)
stack[-1].left = new_left_node
stack.append(new_left_node)
else:
while stack and stack[-1].data < value:
last = stack.pop()
last.right = BST.BinaryTreeNode(value)
stack.append(last.right)
return root
def constructBST(sortedArr):
if len(sortedArr) <= 0:
return None
middle_distance = len(sortedArr) // 2
middle_element = sortedArr[middle_distance]
root = BST.BinaryTreeNode(middle_element)
root.left = constructBST(sortedArr[:middle_distance])
root.right = constructBST(sortedArr[middle_distance + 1:])
return root
def flattenBST(root):
global prev
if root is None:
return
dummy = BST.BinaryTreeNode(-1)
prev = dummy
flattenBSTHelper(root)
prev.left = None
prev.right = None
ret = dummy.right
return ret
