BST Search Operation in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the current node is null in the BST search function.

DSA Typescript

if (node [1] null) {
  return false;
}

Drag options to blanks, or click blank then click option'

A<

B==

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes wrong logic.

Using '>' or '<' to compare with null is incorrect.

We check if the node is equal to null to know if we've reached a leaf without finding the value.

2fill in blank

medium

Complete the code to return true if the current node's value matches the search value.

DSA Typescript

if (node.value [1] value) {
  return true;
}

Drag options to blanks, or click blank then click option'

A<

B!=

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes wrong results.

Using '>' or '<' here is incorrect.

We return true when the node's value equals the value we are searching for.

3fill in blank

hard

Fix the error in the recursive call to search the left subtree when value is less than node's value.

DSA Typescript

if (value [1] node.value) {
  return searchBST(node.left, value);
}

Drag options to blanks, or click blank then click option'

A<

B==

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' causes searching the wrong subtree.

Using '==' or '!=' here is incorrect.

If the value is less than the current node's value, we search the left subtree.

4fill in blank

hard

Fill both blanks to search the right subtree when value is greater than node's value, else return false.

DSA Typescript

if (value [1] node.value) {
  return searchBST(node.right, value);
} else {
  return [2];
}

Drag options to blanks, or click blank then click option'

A>

Btrue

Cfalse

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causes wrong subtree search.

Returning true in else block is incorrect.

If value is greater, search right subtree; otherwise, return false as value not found.

5fill in blank

hard

Fill all three blanks to complete the BST search function with proper conditions and returns.

DSA Typescript

function searchBST(node: TreeNode | null, value: number): boolean {
  if (node [1] null) {
    return false;
  }
  if (node.value [2] value) {
    return true;
  }
  if (value [3] node.value) {
    return searchBST(node.left, value);
  } else {
    return searchBST(node.right, value);
  }
}

Drag options to blanks, or click blank then click option'

A==

B!=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' for null check causes wrong logic.

Using '!=' to compare node.value and value is incorrect.

Using '>' instead of '<' for subtree decision is wrong.

Check if node == null to return false if null, then if node.value == value return true, then if value < node.value search left else right subtree.

Practice

1. What is the main purpose of the search operation in a Binary Search Tree (BST)?

easy

A. To delete a value from the BST

B. To insert a new value into the BST

C. To find whether a given value exists in the BST

D. To traverse all nodes in the BST

Solution

1. Step 1: Understand the purpose of search in BST

   The search operation is designed to check if a specific value is present in the BST.

2. Step 2: Differentiate from other operations

   Insertion adds new values, deletion removes values, and traversal visits all nodes. Search only checks existence.

3. Final Answer:

   To find whether a given value exists in the BST -> Option C

4. Quick Check:

   Search = Find value presence [OK]

Hint: Search checks presence, not insertion or deletion [OK]

Common Mistakes:

• Confusing search with insert or delete
• Thinking search returns all nodes
• Assuming search modifies the tree

2. Which of the following is the correct TypeScript function signature for a BST search method that returns a boolean?

easy

A. function search(root: TreeNode | null, value: number): boolean

B. function search(value: number): TreeNode

C. function search(root: TreeNode, value: string): boolean

D. function search(root: TreeNode | null, value: number): void

Solution

1. Step 1: Analyze parameter types

   The search needs the root node (which can be null) and the value to find (a number).

2. Step 2: Analyze return type

   Search returns true or false, so return type should be boolean.

3. Final Answer:

   function search(root: TreeNode | null, value: number): boolean -> Option A

4. Quick Check:

   Correct params and boolean return [OK]

Hint: Search returns boolean, root can be null [OK]

Common Mistakes:

• Using wrong parameter types
• Returning void instead of boolean
• Using string instead of number for value

3. Given the BST below and the search function call search(root, 7), what will be the output?

BST structure:
10
/ \
5 15
/ \ \
3 7 20

Code snippet:

function search(root: TreeNode | null, value: number): boolean {
  if (!root) return false;
  if (root.val === value) return true;
  if (value < root.val) return search(root.left, value);
  return search(root.right, value);
}

console.log(search(root, 7));

medium

A. false

B. Error

C. undefined

D. true

Solution

1. Step 1: Trace search for value 7

   Start at root 10: 7 < 10, go left to 5. Then 7 > 5, go right to 7.

2. Step 2: Check node value

   Node value is 7, matches search value, so return true.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Found 7 in BST = true [OK]

Hint: Follow BST rules left/right to find value [OK]

Common Mistakes:

• Stopping search too early
• Confusing left and right child directions
• Returning false when node matches

4. The following TypeScript search function for a BST has a bug. What is the error?

function search(root: TreeNode | null, value: number): boolean {
  if (root === null) return false;
  if (root.val === value) return true;
  if (value > root.val) return search(root.left, value);
  else return search(root.right, value);
}

medium

A. The comparison operator should be >= instead of >

B. The recursive calls to left and right children are swapped

C. The function does not return a boolean

D. The base case is missing

Solution

1. Step 1: Check recursive calls logic

   For BST, if value > root.val, search should go right, but code goes left.

2. Step 2: Confirm swapped children calls

   Similarly, else goes right instead of left. So left and right calls are swapped.

3. Final Answer:

   The recursive calls to left and right children are swapped -> Option B

4. Quick Check:

   Left/right calls swapped = bug [OK]

Hint: Value > root goes right, not left [OK]

Common Mistakes:

• Mixing left and right child in recursion
• Ignoring base case (though present here)
• Wrong comparison operators

5. You want to search for a value in a BST that may contain duplicate values on the right subtree. Which modification to the standard BST search logic ensures you find the first occurrence of the value?

Choose the correct approach:

hard

A. Always search left subtree when value equals current node's value

B. Return true immediately when value equals current node's value

C. Search right subtree when value equals current node's value to find duplicates

D. Traverse entire tree inorder to find all occurrences

Solution

1. Step 1: Understand duplicate placement in BST

   Duplicates are stored in right subtree, so first occurrence is the leftmost matching node.

2. Step 2: Modify search to find first occurrence

   When value equals current node, continue searching left subtree to find earlier occurrence.

3. Final Answer:

   Always search left subtree when value equals current node's value -> Option A

4. Quick Check:

   Search left on equal to find first duplicate [OK]

Hint: On equal, go left to find first duplicate [OK]

Common Mistakes:

• Stopping search immediately on equal
• Searching right subtree on equal
• Doing full inorder traversal unnecessarily