Easy
Given the root of a binary tree, return its maximum depth.
A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 3
Example 2:
Input: root = [1,null,2]
Output: 2
Constraints:
[0, 104].-100 <= Node.val <= 100/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function(root) {
    return findDepth(root, 0)
};
var findDepth = function(node, currentDepth) {
    if (!node) {
        return 0
    }
    currentDepth++
    return 1 + Math.max(findDepth(node.left, currentDepth), findDepth(node.right, currentDepth))
};
export { maxDepth }