https://leetcode.com/problems/kth-smallest-element-in-a-bst/

Author: harshitgindra

LeetCodeSolutions/BinarySearchTree/KthSmallestElementInABst.cs

@@ -0,0 +1,43 @@
+namespace LeetCodeSolutions.BinarySearchTree;
+
+public class KthSmallestElementInABst
+{
+    public int KthSmallest(TreeNode root, int k)
+    {
+        Stack<int> stack = new Stack<int>();
+        DFS(root, k, stack);
+        return stack.Pop();
+    }
+
+    private void DFS(TreeNode node, int k, Stack<int> stack)
+    {
+        if (node != null)
+        {
+            DFS(node.left, k, stack);
+            if (stack.Count < k)
+            {
+                stack.Push(node.val);
+                DFS(node.right, k, stack);
+            }
+        }
+    }
+
+    [Test(Description = "https://leetcode.com/problems/kth-smallest-element-in-a-bst/")]
+    [Category("Medium")]
+    [Category("LeetCode")]
+    [Category("Kth smallest element in a BST")]
+    [TestCaseSource(nameof(Input))]
+    [Category("Binary Search Tree")]
+    [Category("TopInterview")]
+    public void Test1((int Output, (int?[], int) Input) item)
+    {
+        var response = KthSmallest(item.Input.Item1.ToTreeNode(), item.Input.Item2);
+        Assert.That(response, Is.EqualTo(item.Output));
+    }
+
+    public static IEnumerable<(int Output, (int?[], int) Input)> Input =>
+        new List<(int, (int?[], int))>()
+        {
+            (3, ([5, 3, 6, 2, 4, null, null, 1], 3)), 
+        };
+}

README.md

@@ -140,7 +140,7 @@ The Top Interview 150 collection on Leetcode is a curated set of 150 interview q
 | 103                                           | Binary Tree Zigzag Level Order Traversal                                                                  | Medium     |    ✅    |
 | <br>        Binary Search Tree<br>           |                                                                                                           |            |        |
 | 86                                           | Minimum Absolute Difference in BST                                                                        | Easy       |    ✅    |
-| 87                                           | Kth Smallest Element in a BST                                                                             | Medium     |        |
+| 87                                           | Kth Smallest Element in a BST                                                                             | Medium     |    ✅    |
 | 98                                           | Validate Binary Search Tree                                                                               | Medium     |   ✅     |
 | <br>        Graph General<br>                |                                                                                                           |            |        |
 | 200                                           | Number of Islands                                                                                         | Medium     |   ✅     |