---
# System prepended metadata

title: Kth Smallest Element in a BST
tags: [Medium, Tree]

---

# Kth Smallest Element in a BST
###### tags: `Medium` `Tree`
>question : https://leetcode.com/explore/interview/card/top-interview-questions-medium/108/trees-and-graphs/790/

>reference : 

>related problem : 
## My Solution
```java=
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private Stack<TreeNode> stack;
    public int kthSmallest(TreeNode root, int k) {
        stack = new Stack<TreeNode>();
        toTheLastLeftNode(root);
        TreeNode ans = new TreeNode();
        for(int i = 0; i < k; i++) {
            ans = stack.pop();
            if(ans.right != null)
                toTheLastLeftNode(ans.right);
        }
        return ans.val;
    }
    
    private void toTheLastLeftNode(TreeNode node) {
        while(node != null) {
            stack.add(node);
            node = node.left;
        }
    }
}
```
## Other Solution

## K-th largest in BST
![](https://i.imgur.com/Ra4PHGw.png)
