104-maximum-depth-of-binary-tree.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
const maxDepth = function(root) {
  if (!root) return 0;
  const left = maxDepth(root.left);
  const right = maxDepth(root.right);
  let depth = left > right ? left : right;
  return (depth += 1);
};