Search for a Value in Linked List in DSA Go - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Searching a Value in a Linked List

What is the output of the following Go code that searches for a value in a singly linked list?

DSA Go

package main
import "fmt"
type Node struct {
    value int
    next  *Node
}
func search(head *Node, target int) bool {
    current := head
    for current != nil {
        if current.value == target {
            return true
        }
        current = current.next
    }
    return false
}
func main() {
    n3 := &Node{value: 3, next: nil}
    n2 := &Node{value: 2, next: n3}
    n1 := &Node{value: 1, next: n2}
    fmt.Println(search(n1, 2))
}

A compilation error

B false

C true

D runtime error

💡 Hint

Trace the linked list nodes and check if the target value exists.

The search function traverses the linked list starting from the head node. It checks each node's value. Since the value 2 exists in the list, the function returns true.

❓ Predict Output

intermediate

Output when Searching a Non-Existent Value

What will be printed when searching for a value that is not in the linked list?

DSA Go

package main
import "fmt"
type Node struct {
    value int
    next  *Node
}
func search(head *Node, target int) bool {
    current := head
    for current != nil {
        if current.value == target {
            return true
        }
        current = current.next
    }
    return false
}
func main() {
    n3 := &Node{value: 3, next: nil}
    n2 := &Node{value: 2, next: n3}
    n1 := &Node{value: 1, next: n2}
    fmt.Println(search(n1, 5))
}

A false

B true

C nil

D panic: runtime error

💡 Hint

Check if the target value exists in any node.

The value 5 is not present in the linked list, so the search function returns false.

🧠 Conceptual

advanced

Understanding Search Time Complexity in Linked Lists

What is the time complexity of searching for a value in a singly linked list of n nodes?

A O(1) - Constant time

B O(n) - Linear time

C O(log n) - Logarithmic time

D O(n^2) - Quadratic time

💡 Hint

Consider how many nodes might need to be checked in the worst case.

In the worst case, the search function may need to check every node once, resulting in linear time complexity O(n).

❓ Predict Output

advanced

Output of Search Function with Nil Head

What will be the output when the search function is called with a nil (empty) linked list?

DSA Go

package main
import "fmt"
type Node struct {
    value int
    next  *Node
}
func search(head *Node, target int) bool {
    current := head
    for current != nil {
        if current.value == target {
            return true
        }
        current = current.next
    }
    return false
}
func main() {
    var head *Node = nil
    fmt.Println(search(head, 1))
}

A compilation error

B true

C panic: runtime error

D false

💡 Hint

An empty list means no nodes to check.

Since the list is empty (head is nil), the search function immediately returns false.

🔧 Debug

expert

Identify the Bug in the Search Function

Consider this modified search function. What error will it cause when searching a linked list?

DSA Go

func search(head *Node, target int) bool {
    current := head
    for current.next != nil {
        if current.value == target {
            return true
        }
        current = current.next
    }
    return false
}

A It will cause a runtime panic when the list is empty (nil head).

B It will always return true regardless of the list content.

C It will never find the target even if it exists.

D It will cause a compilation error due to syntax.

💡 Hint

Check the loop condition and what happens if head is nil.

The loop condition current.next != nil assumes current is not nil. If head is nil, accessing current.next causes a runtime panic.

Practice

1. What is the main purpose of searching for a value in a linked list?

easy

A. To reverse the order of nodes in the list

B. To add a new node at the end of the list

C. To delete the first node of the list

D. To find if a specific value exists in the list

Solution

1. Step 1: Understand the search operation

   Searching means checking each node to see if it contains the target value.

2. Step 2: Identify the goal of searching

   The goal is to find whether the value exists anywhere in the linked list.

3. Final Answer:

   To find if a specific value exists in the list -> Option D

4. Quick Check:

   Search means find value presence = To find if a specific value exists in the list [OK]

Hint: Search means look for a value in nodes [OK]

Common Mistakes:

• Confusing search with insertion or deletion
• Thinking search changes the list structure
• Assuming search reverses the list

2. Which of the following Go code snippets correctly checks if a linked list node's value equals the target value val?

easy

A. if current.val = val { return true }

B. if current.value == val { return true }

C. if current.value := val { return true }

D. if current.value != val { return true }

Solution

1. Step 1: Identify correct equality check syntax in Go

   Use double equals (==) to compare values, not single equals (=) or :=.

2. Step 2: Check the field name and comparison logic

   Assuming node field is 'value', 'current.value == val' correctly compares values.

3. Final Answer:

   if current.value == val { return true } -> Option B

4. Quick Check:

   Use '==' for comparison in Go [OK]

Hint: Use '==' to compare values, not '=' or ':=' [OK]

Common Mistakes:

• Using '=' instead of '==' for comparison
• Using ':=' inside if condition incorrectly
• Checking inequality instead of equality

3. What will be the output of the following Go code that searches for value 5 in a linked list?

type Node struct {
    value int
    next  *Node
}

func search(head *Node, val int) bool {
    current := head
    for current != nil {
        if current.value == val {
            return true
        }
        current = current.next
    }
    return false
}

// List: 1 -> 3 -> 5 -> 7 -> nil
head := &Node{1, &Node{3, &Node{5, &Node{7, nil}}}}
fmt.Println(search(head, 5))

medium

A. true

B. false

C. Compilation error

D. Runtime panic

Solution

1. Step 1: Trace the search function through the list

   It checks nodes 1, 3, then 5. When it finds 5, it returns true immediately.

2. Step 2: Confirm no errors occur

   Code is correct and will print true because 5 exists in the list.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Value 5 found in list = true [OK]

Hint: Stop search when value found, else false [OK]

Common Mistakes:

• Assuming search returns false if value is in list
• Thinking code causes panic due to nil pointer
• Confusing output with string instead of boolean

4. Identify the bug in this Go function that searches for a value in a linked list:

func search(head *Node, val int) bool {
    current := head
    for current.next != nil {
        if current.value == val {
            return true
        }
        current = current.next
    }
    return false
}

medium

A. Loop condition misses checking the last node

B. Comparison uses '=' instead of '=='

C. Function returns true even if value not found

D. Variable 'current' is not initialized

Solution

1. Step 1: Analyze the loop condition

   The loop runs while current.next != nil, so it stops before last node.

2. Step 2: Understand impact on search

   The last node's value is never checked, so search can miss the value if it's there.

3. Final Answer:

   Loop condition misses checking the last node -> Option A

4. Quick Check:

   Loop must check all nodes including last [OK]

Hint: Use 'current != nil' to check all nodes [OK]

Common Mistakes:

• Using current.next != nil instead of current != nil
• Forgetting to check last node's value
• Misreading loop condition as correct

5. Given a linked list where nodes may contain duplicate values, how would you modify the search function to return the count of occurrences of a target value val instead of just true/false?
Choose the correct approach.

hard

A. Return true immediately when first node.value == val is found

B. Use recursion to return true if any node.value == val

C. Traverse all nodes, increment count when node.value == val, return count

D. Stop traversal when node.value != val is found

Solution

1. Step 1: Understand requirement to count all occurrences

   We must check every node because duplicates can appear anywhere.

2. Step 2: Modify search to count matches

   Traverse all nodes, increase count each time node.value equals val, then return count.

3. Final Answer:

   Traverse all nodes, increment count when node.value == val, return count -> Option C

4. Quick Check:

   Count all matches by full traversal [OK]

Hint: Count matches by checking every node [OK]

Common Mistakes:

• Stopping search after first match
• Returning boolean instead of count
• Ignoring duplicates in list