623. Add One Row to Tree

Medium

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Given the root of a binary tree and two integers val and depth, add a row of nodes with value val at the given depth depth.

Note that the root node is at depth 1.

The adding rule is:

• Given the integer depth, for each not null tree node cur at the depth depth - 1, create two tree nodes with value val as cur's left subtree root and right subtree root.

• cur's original left subtree should be the left subtree of the new left subtree root.

• cur's original right subtree should be the right subtree of the new right subtree root.

• If depth == 1 that means there is no depth depth - 1 at all, then create a tree node with value val as the new root of the whole original tree, and the original tree is the new root's left subtree.

Example 1:

Input: root = [4,2,6,3,1,5], val = 1, depth = 2
Output:
 [4,1,1,2,null,null,6,3,1,5]

Example 2:

Input: root = [4,2,null,3,1], val = 1, depth = 3
Output:
 [4,2,null,1,1,3,null,null,1]

Constraints:

• The number of nodes in the tree is in the range [1, 104].

• The depth of the tree is in the range [1, 104].

• -100 <= Node.val <= 100

• -105 <= val <= 105

• 1 <= depth <= the depth of tree + 1

class Solution:
    def addOneRow(self, root: Optional[TreeNode], val: int, depth: int) -> Optional[TreeNode]:
        if not root or depth <= 0 : return None
        if depth == 1:
            return TreeNode(val, root, None)
        if depth == 2:
            root.left = TreeNode(val, root.left, None)
            root.right = TreeNode(val, None, root.right)
        else:
            root.left = self.addOneRow(root.left, val,  depth-1)
            root.right = self.addOneRow(root.right, val,  depth-1)
        return root