Tree: Depth-First Search - Binary Tree Postorder Traversal
Given the following iterative postorder traversal code, what is the final output when run on the tree: root = TreeNode(1, None, TreeNode(2, TreeNode(3)))?
def postorderTraversal(root):
result = []
stack = []
last_visited = None
current = root
while current or stack:
while current:
stack.append(current)
current = current.left
peek_node = stack[-1]
if peek_node.right and last_visited != peek_node.right:
current = peek_node.right
else:
result.append(peek_node.val)
last_visited = stack.pop()
return result