104.js

/** ------------------------------------------------------------------------------
 * 
 * 104. Maximum Depth of Binary Tree
 * Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree
 * https://leetcode.com/problems/maximum-depth-of-binary-tree/description/
 * 
 ------------------------------------------------------------------------------ */
/**
 * 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) {
  if (!root) return 0
  const left = maxDepth(root.left)
  const right = maxDepth(root.right)

  return Math.max(left, right) + 1
}

console.log(maxDepth([3, 9, 20, null, null, 15, 7]))