kthSmallest

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} k
 * @return {number}
 */
var kthSmallest = function(root, k) {
    if (k === 1 && root) {
        return root.val
    } else if (!root.left && !root.right && k > 1) {
        return null;  
    } else {
        return kthSmallest(root.left, k - 1) || kthSmallest(root.right, k - 3);
    }
         

};