Boundary of Binary Tree

7class Solution:
●    def boundaryOfBinaryTree(self, root):
9        if not root:
......
11        result = []
12        # Add root if not leaf
13        if not self.isLeaf(root):
......
16        self.addLeftBoundary(root.left, result)
17        # Collect all leaves (left-to-right)
18        self.addLeaves(root, result)
19        # Collect right boundary (bottom-up, no leaves)
20        self.addRightBoundary(root.right, result)
21        return result
22 
......
27        while node:
28            if not self.isLeaf(node):
29                result.append(node.val)
......
35        if self.isLeaf(node):
36            result.append(node.val)
37            return
......
43        while node:
44            if not self.isLeaf(node):
45                stack.append(node.val)
......
47        # Add in reverse (bottom-up)
48        while stack:
49            result.append(stack.pop())