BST Search Operation in DSA Go - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of BST Search for Existing Value

What is the output of the following Go code that searches for the value 15 in a BST?

DSA Go

package main
import "fmt"
type Node struct {
    val   int
    left  *Node
    right *Node
}
func searchBST(root *Node, target int) *Node {
    if root == nil || root.val == target {
        return root
    }
    if target < root.val {
        return searchBST(root.left, target)
    }
    return searchBST(root.right, target)
}
func main() {
    root := &Node{val: 10}
    root.left = &Node{val: 5}
    root.right = &Node{val: 20}
    root.right.left = &Node{val: 15}
    result := searchBST(root, 15)
    if result != nil {
        fmt.Println(result.val)
    } else {
        fmt.Println("Not found")
    }
}

A 15

B 20

C 5

D Not found

💡 Hint

Trace the search path comparing target with node values.

The search starts at root (10). Since 15 > 10, it moves to right subtree (20). Since 15 < 20, it moves to left subtree of 20 (15). The code correctly finds 15.

❓ Predict Output

intermediate

Output of BST Search for Non-Existing Value

What is the output of the following Go code that searches for the value 17 in a BST?

DSA Go

package main
import "fmt"
type Node struct {
    val   int
    left  *Node
    right *Node
}
func searchBST(root *Node, target int) *Node {
    if root == nil || root.val == target {
        return root
    }
    if target < root.val {
        return searchBST(root.left, target)
    }
    return searchBST(root.right, target)
}
func main() {
    root := &Node{val: 10}
    root.left = &Node{val: 5}
    root.right = &Node{val: 20}
    root.right.left = &Node{val: 15}
    result := searchBST(root, 17)
    if result != nil {
        fmt.Println(result.val)
    } else {
        fmt.Println("Not found")
    }
}

A 15

B 5

C 20

D Not found

💡 Hint

Check if the value 17 exists in the tree by following the search path.

The search starts at root (10). Since 17 > 10, it moves to right subtree (20). Since 17 < 20, it moves to left subtree of 20 (15). Since 17 > 15, it moves to right subtree of 15, which is nil. So, the value 17 is not found in the BST.

🧠 Conceptual

advanced

Understanding BST Search Path

In a BST, which path does the search algorithm follow to find a target value?

A Go left if target is less than current node, else go right

B Go right if target is less than current node, else go left

C Always go left child regardless of target value

D Search both left and right subtrees simultaneously

💡 Hint

Think about how BST property orders values.

BST property: left child values are less, right child values are greater. So search goes left if target is smaller, right if larger.

🔧 Debug

advanced

Identify the Bug in BST Search Code

What error will the following Go code produce when searching for a value in a BST?

DSA Go

package main
import "fmt"
type Node struct {
    val   int
    left  *Node
    right *Node
}
func searchBST(root *Node, target int) *Node {
    if root == nil {
        return nil
    }
    if root.val == target {
        return root
    }
    if target > root.val {
        return searchBST(root.left, target)
    }
    return searchBST(root.right, target)
}
func main() {
    root := &Node{val: 10}
    root.left = &Node{val: 5}
    root.right = &Node{val: 20}
    result := searchBST(root, 5)
    if result != nil {
        fmt.Println(result.val)
    } else {
        fmt.Println("Not found")
    }
}

A Prints 20

B Prints 5

C Prints "Not found"

D Compilation error

💡 Hint

Check the direction of recursive calls for target > root.val.

The code incorrectly calls searchBST on root.left when target > root.val, which should be root.right. When searching for 5 (< 10), since the condition target > root.val is false, it takes the else branch and searches root.right instead of root.left, missing the node 5 and printing "Not found".

🚀 Application

expert

Number of Nodes Visited in BST Search

Given a BST with nodes inserted in this order: 10, 5, 15, 3, 7, 12, 18. How many nodes will be visited when searching for the value 7?

A 4

B 3

C 2

D 5

💡 Hint

Trace the search path from root to the target node counting nodes visited.

Search path: 10 (root) -> 5 (left child) -> 7 (right child of 5). Total nodes visited = 3.

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