二叉树的最大深度

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */

var maxDepth = function(root) {
  let temp = [];
    if(!root){
        return 0;
    }
    var check = function(root,k){
        if(!root.left&&!root.right){
            temp.push(++k);
            return ;
        }
        //左子树
        if(root.left){
            check(root.left,k+1);
        }
        if(root.right){
            check(root.right,k+1);
        }
    }
    check(root,0);
    return Math.max(...temp);
};