Inorder traversal and stop at kth smallest element

[chetak-gmail.com]

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int KthSmallest(TreeNode root, int k) {
        return KthSmallest_helper(root, ref k).val;
    }
    public TreeNode KthSmallest_helper(TreeNode root, ref int k) {
        if(root == null) return null;
        TreeNode num = KthSmallest_helper(root.left, ref k);
        if(num != null) return num;
        k--;
        if(k == 0)
        {
            return root;
        }
        num = KthSmallest_helper(root.right, ref k);
        if(num != null) return num;
        return null;
    }
}```