BST Search Operation in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Go

if root [1] nil {
    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 comparison operators like '<' or '>' with nil causes errors.

We check if the current node is nil to know if the search reached a leaf without finding the value.

2fill in blank

medium

Complete the code to compare the search value with the current node's data.

DSA Go

if root.data [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 incorrect search results.

Using '<' or '>' here is incorrect for equality check.

If the current node's data equals the search value, we found the value in the BST.

3fill in blank

hard

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

DSA Go

if value [1] root.data {
    return searchBST(root.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 logically incorrect.

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

4fill in blank

hard

Fill both blanks to complete the recursive search for the right subtree when value is greater than current node's data.

DSA Go

if value [1] root.data {
    return searchBST(root.[2], value)
}

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

A<

Bright

C>

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using 'left' instead of 'right' causes wrong subtree search.

If value is greater than current node's data, search the right subtree.

5fill in blank

hard

Fill all three blanks to complete the full BST search function in Go.

DSA Go

func searchBST(root *Node, value int) bool {
    if root [1] nil {
        return false
    }
    if root.data [2] value {
        return true
    }
    if value [3] root.data {
        return searchBST(root.left, value)
    } else {
        return searchBST(root.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 nil check.

Using '!=' instead of '==' for data equality.

Using '>' instead of '<' for left subtree search.

The function checks if root is nil, then if root.data equals value, then searches left if value is less, else right.

Practice

1. What does the search operation in a Binary Search Tree (BST) do?

easy

A. Finds whether a given value exists in the BST

B. Deletes a node from the BST

C. Inserts a new node into the BST

D. Traverses all nodes in the BST

Solution

1. Step 1: Understand the purpose of BST search

   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 nodes, deletion removes nodes, and traversal visits nodes. Search only checks for existence.

3. Final Answer:

   Finds whether a given value exists in the BST -> Option A

4. Quick Check:

   Search = Find value [OK]

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

Common Mistakes:

• Confusing search with insert or delete
• Thinking search returns the node always
• Assuming search traverses all nodes

2. Which of the following is the correct Go function signature for a BST search method that returns a boolean indicating if a value exists?

easy

A. func Search(val int) *Node

B. func (root *Node) Search(val int) bool

C. func (root Node) Search(val string) bool

D. func Search(root Node, val int) int

Solution

1. Step 1: Identify method receiver and return type

   BST search is usually a method on a pointer to Node and returns bool for found or not.

2. Step 2: Check parameter types and return type

   func (root *Node) Search(val int) bool uses pointer receiver, int parameter, and bool return which matches the expected signature.

3. Final Answer:

   func (root *Node) Search(val int) bool -> Option B

4. Quick Check:

   Pointer receiver + bool return = func (root *Node) Search(val int) bool [OK]

Hint: Search returns bool, uses pointer receiver for tree nodes [OK]

Common Mistakes:

• Using value receiver instead of pointer
• Wrong parameter or return types
• Confusing method vs function signatures

3. Given the BST below and the Go code snippet, what will be the output? BST structure: ``` 10 / \ 5 15 / 3 ``` Go code:

found := root.Search(3)
fmt.Println(found)

medium

A. true

B. false

C. nil

D. runtime error

Solution

1. Step 1: Trace the search for value 3 in the BST

   Starting at root 10, 3 < 10, go left to 5; 3 < 5, go left to 3; found node with value 3.

2. Step 2: Understand the returned value and print output

   Search returns true because 3 exists; printing true outputs 'true'.

3. Final Answer:

   true -> Option A

4. Quick Check:

   3 found in BST = true [OK]

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

Common Mistakes:

• Assuming search returns node instead of bool
• Confusing true/false output
• Ignoring BST structure when tracing

4. The following Go code for BST search has a bug. What is the bug?

func (root *Node) Search(val int) bool {
    if root == nil {
        return false
    }
    if root.Value == val {
        return true
    }
    if val < root.Value {
        return root.Search(val)
    } else {
        return root.Search(val)
    }
}

medium

A. Base case for nil root is missing

B. Uses value receiver instead of pointer

C. Returns int instead of bool

D. Recursive calls do not move to left or right child nodes

Solution

1. Step 1: Analyze recursive calls in search method

   Both recursive calls use root.Search(val) without moving to root.Left or root.Right, causing infinite recursion.

2. Step 2: Identify correct recursive calls

   Should call root.Left.Search(val) if val < root.Value, else root.Right.Search(val) to move down the tree.

3. Final Answer:

   Recursive calls do not move to left or right child nodes -> Option D

4. Quick Check:

   Recursive calls must move down tree [OK]

Hint: Recursive calls must go to left or right child [OK]

Common Mistakes:

• Calling search on same node causing infinite loop
• Missing base case for nil
• Wrong return types

5. You want to search for a value in a BST but also count how many nodes you visited during the search. Which modification to the search function is best?

hard

A. Use a global variable to count nodes visited during search

B. Return the node instead of bool and count nodes outside the function

C. Add a counter parameter passed by pointer and increment it on each node visited

D. Modify the BST to store counts in each node

Solution

1. Step 1: Understand the need to count nodes during search

   Counting nodes visited requires tracking each node checked during recursion.

2. Step 2: Choose method to count nodes visited

   Passing a pointer to a counter variable and incrementing it at each node visit allows accurate counting without side effects.

3. Final Answer:

   Add a counter parameter passed by pointer and increment it on each node visited -> Option C

4. Quick Check:

   Pass counter pointer to track visits [OK]

Hint: Pass counter pointer to track nodes visited [OK]

Common Mistakes:

• Using global variables causing side effects
• Counting outside search missing recursive visits
• Changing BST structure unnecessarily