From fede86e1bba7fe6cbe2fcf8dc2eca0c156d7315a Mon Sep 17 00:00:00 2001
From: Peter Chen <sanpeter992000@gmail.com>
Date: Sat, 1 Nov 2025 11:10:06 +0800
Subject: [PATCH 1/2] Add unit tests for the "Kth Smallest Element in a BST"
 problem.

---
 src/KthSmallestElementInaBST230.java          | 30 ------------
 .../medium/KthSmallestElementInABST230.java   | 28 +++++++++++
 .../KthSmallestElementInABST230Test.java      | 48 +++++++++++++++++++
 3 files changed, 76 insertions(+), 30 deletions(-)
 delete mode 100644 src/KthSmallestElementInaBST230.java
 create mode 100644 src/main/java/com/leetcode/medium/KthSmallestElementInABST230.java
 create mode 100644 src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java

diff --git a/src/KthSmallestElementInaBST230.java b/src/KthSmallestElementInaBST230.java
deleted file mode 100644
index 070bdf7..0000000
--- a/src/KthSmallestElementInaBST230.java
+++ /dev/null
@@ -1,30 +0,0 @@
-// Tree, Depth-First Search, Binary Search Tree, Binary Tree
-
-import java.util.List;
-import java.util.ArrayList;
-
-public class KthSmallestElementInaBST230 {
-    private void inorder(TreeNode node, List<Integer> res) {
-        if (node == null) {
-            return;
-        }
-        this.inorder(node.left, res);
-        res.add(node.val);
-        this.inorder(node.right, res);
-    }
-    /*
-        Time complexity : O(N) to build a traversal.
-        Space complexity : O(N) to keep an inorder traversal.
-     */
-    public int kthSmallest(TreeNode root, int k) {
-        List<Integer> res = new ArrayList<>();
-        this.inorder(root, res);
-        return res.get(k - 1);
-    }
-
-    public static void main(String[] args) {
-        TreeNode root = new TreeNode(3, new TreeNode(1, null, new TreeNode(2)), new TreeNode(4));
-        int k = 1;
-        System.out.println(new KthSmallestElementInaBST230().kthSmallest(root, k)); // 1
-    }
-}
diff --git a/src/main/java/com/leetcode/medium/KthSmallestElementInABST230.java b/src/main/java/com/leetcode/medium/KthSmallestElementInABST230.java
new file mode 100644
index 0000000..0a0b393
--- /dev/null
+++ b/src/main/java/com/leetcode/medium/KthSmallestElementInABST230.java
@@ -0,0 +1,28 @@
+// Tags: Tree, Binary Search Tree, DFS
+package com.leetcode.medium;
+
+import com.leetcode.datastructure.TreeNode;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class KthSmallestElementInABST230 {
+    private void inorder(TreeNode node, List<Integer> res) {
+        if (node == null) {
+            return;
+        }
+        inorder(node.left, res);
+        res.add(node.val);
+        inorder(node.right, res);
+    }
+
+    /*
+        Time complexity : O(N) to build a traversal.
+        Space complexity : O(N) to keep an inorder traversal.
+     */
+    public int kthSmallest(TreeNode root, int k) {
+        List<Integer> values = new ArrayList<>();
+        inorder(root, values);
+        return values.get(k - 1);
+    }
+}
diff --git a/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java b/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java
new file mode 100644
index 0000000..11dc53d
--- /dev/null
+++ b/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java
@@ -0,0 +1,48 @@
+package com.leetcode.medium;
+
+import com.leetcode.datastructure.TreeNode;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class KthSmallestElementInABST230Test {
+    private KthSmallestElementInABST230 solution;
+
+    @BeforeEach
+    public void setUp() {
+        solution = new KthSmallestElementInABST230();
+    }
+
+    @Test
+    void testKthSmallest_Example1() {
+        TreeNode root = new TreeNode(3,
+                new TreeNode(1, null, new TreeNode(2)),
+                new TreeNode(4));
+
+        int k = 1;
+
+        int expected = 1;
+        int result = solution.kthSmallest(root, k);
+
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testKthSmallest_Example2() {
+        TreeNode root = new TreeNode(5,
+                new TreeNode(3,
+                        new TreeNode(2,
+                                new TreeNode(1),
+                                null),
+                        new TreeNode(4)),
+                new TreeNode(6));
+
+        int k = 3;
+
+        int expected = 3;
+        int result = solution.kthSmallest(root, k);
+
+        assertEquals(expected, result);
+    }
+}

From 374cd46603411e8e5b2f3fe5631333b956b6b23f Mon Sep 17 00:00:00 2001
From: Peter Chen <sanpeter992000@gmail.com>
Date: Sat, 1 Nov 2025 11:15:36 +0800
Subject: [PATCH 2/2] Remove public modifier from setUp method in
 KthSmallestElementInABST230Test.

---
 .../com/leetcode/medium/KthSmallestElementInABST230Test.java    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java b/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java
index 11dc53d..9ac42c2 100644
--- a/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java
+++ b/src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java
@@ -10,7 +10,7 @@ public class KthSmallestElementInABST230Test {
     private KthSmallestElementInABST230 solution;
 
     @BeforeEach
-    public void setUp() {
+    void setUp() {
         solution = new KthSmallestElementInABST230();
     }