Given the `root`

of a binary tree, return *the average value of the nodes on each level in the form of an array*. Answers within `10`

of the actual answer will be accepted.
^{-5}

**Example 1:**

Input:root = [3,9,20,null,15,7]Output:[3.00000,14.50000,11.00000] Explanation: The average value of nodes on level 0 is 3, on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

**Example 2:**

Input:root = [3,9,20,15,7]Output:[3.00000,14.50000,11.00000]

**Constraints:**

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

.^{4}] `-2`

^{31}<= Node.val <= 2^{31}- 1