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 = 2Output:[4,1,1,2,null,null,6,3,1,5]

**Example 2:**

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

**Constraints:**

- The number of nodes in the tree is in the range
`[1, 10`

.^{4}] - The depth of the tree is in the range
`[1, 10`

.^{4}] `-100 <= Node.val <= 100`

`-10`

^{5}<= val <= 10^{5}`1 <= depth <= the depth of tree + 1`