Kth Smallest Element in a BST

Inorder Traverse

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public int kthSmallest(TreeNode root, int k) {        Stack<TreeNode> s = new Stack<TreeNode>();                TreeNode node = root;        int result = -1;                while (!s.isEmpty() || node != null) {            if (node != null) {                s.push(node);                node = node.left;            } else {                node = s.pop();                k--;                if (k == 0) {                    return node.val;                }                node = node.right;            }        }        return result;    }}

Data Structure Augmentation