104.Tree.E-maximumDepthOfBinaryTree.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 * 
 * Given a binary tree, find its maximum depth.
 * The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
 * 输入: root = [3,9,20,null,null,15,7]
 * 输出: depth=3
 */

/**
 * @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
};