Given the `root` of a binary tree, the depth of each node is the shortest distance to the root.

Return the smallest subtree such that it contains all the deepest nodes in the original tree.

A node is called the deepest if it has the largest depth possible among any node in the entire tree.

The subtree of a node is a tree consisting of that node, plus the set of all descendants of that node.

Example 1:

    Input: root = [3,5,1,6,2,0,8,null,null,7,4]
    Output: [2,7,4]
    Explanation: We return the node with value 2, colored in yellow in the diagram.
    The nodes coloured in blue are the deepest nodes of the tree.
    Notice that nodes 5, 3 and 2 contain the deepest nodes in the tree but node 2 is the smallest subtree among them, so we return it.

Example 2:

    Input: root = [1]
    Output: [1]
    Explanation: The root is the deepest node in the tree.

Example 3:

    Input: root = [0,1,3,null,2]
    Output: [2]
    Explanation: The deepest node in the tree is 2, the valid subtrees are the subtrees of nodes 2, 1 and 0 but the subtree of node 2 is the smallest.

Constraints:

- The number of nodes in the tree will be in the range `[1, 500]`.
- `0 <= Node.val <= 500`
- The values of the nodes in the tree are unique.

Note: This question is the same as 1123: https://leetcode.com/problems/lowest-common-ancestor-of-deepest-leaves/