Solution2.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def addOneRow(
        self, root: Optional[TreeNode], val: int, depth: int
    ) -> Optional[TreeNode]:
        if depth == 1:
            return TreeNode(val, root)
        q = deque([root])
        i = 0
        while q:
            i += 1
            for _ in range(len(q)):
                node = q.popleft()
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
                if i == depth - 1:
                    node.left = TreeNode(val, node.left, None)
                    node.right = TreeNode(val, None, node.right)
        return root