LC 104. Maximum Depth of Binary Tree

 1/**
 2 * Definition for a binary tree node.
 3 * function TreeNode(val, left, right) {
 4 *     this.val = (val===undefined ? 0 : val)
 5 *     this.left = (left===undefined ? null : left)
 6 *     this.right = (right===undefined ? null : right)
 7 * }
 8 */
 9/**
10 * @param {TreeNode} root
11 * @return {number}
12 */
13var maxDepth = function(root) {
14  if (!root) {
15    return 0
16  } else {
17    const left = maxDepth(root.left)
18    const right = maxDepth(root.right)
19    return Math.max(left, right) + 1
20  }
21};