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Add unit tests for the "Kth Smallest Element in a BST" problem. #32

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Merged
kobukuro merged 2 commits into from
Nov 1, 2025
Merged

Add unit tests for the "Kth Smallest Element in a BST" problem. #32

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fede86e
Add unit tests for the "Kth Smallest Element in a BST" problem.
kobukuro Nov 1, 2025
374cd46
Remove public modifier from setUp method in KthSmallestElementInABST2…
kobukuro Nov 1, 2025
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30 changes: 0 additions & 30 deletions src/KthSmallestElementInaBST230.java
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28 changes: 28 additions & 0 deletions src/main/java/com/leetcode/medium/KthSmallestElementInABST230.java
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Original file line number Diff line number Diff line change
@@ -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);
}
Comment on lines +26 to +27

Copilot AI Nov 1, 2025

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The method lacks validation for the parameter k. If k is less than 1 or greater than the number of nodes in the tree, this will throw an IndexOutOfBoundsException. Consider adding validation to check that k is within the valid range (1 <= k <= tree size) and throw a more meaningful exception (e.g., IllegalArgumentException) with a descriptive error message.

Suggested change
return values.get(k - 1);
}
if (k < 1 || k > values.size()) {
throw new IllegalArgumentException("Parameter k is out of bounds. Valid range: 1 <= k <= " + values.size() + ", but got k = " + k);
}
return values.get(k - 1);

Copilot uses AI. Check for mistakes.
}
48 changes: 48 additions & 0 deletions src/test/java/com/leetcode/medium/KthSmallestElementInABST230Test.java
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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
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);
}
}