Search for a Value in Linked List in DSA C# - Build from Scratch

Search for a Value in Linked List

📖 Scenario: You are working on a simple contact list app. Each contact is stored as a node in a linked list. You want to find if a contact with a specific name exists in the list.

🎯 Goal: Build a linked list of contacts and write code to search for a contact by name.

📋 What You'll Learn

Create a linked list with exactly three nodes containing the names: "Alice", "Bob", and "Charlie" in that order.

Create a variable called searchName and set it to "Bob".

Write a loop to search the linked list for a node with the name equal to searchName.

Print "Found" if the name is found, otherwise print "Not Found".

💡 Why This Matters

🌍 Real World

Linked lists are used in many apps to store ordered data where you need to add or remove items efficiently, like contact lists or playlists.

💼 Career

Understanding linked lists and how to search them is a fundamental skill for software developers, especially for roles involving data structures and algorithms.

1

Create the linked list nodes

Create a class called Node with a public string field name and a public Node field next. Then create three nodes with names "Alice", "Bob", and "Charlie". Link them so that head points to the first node.

DSA C#

// Define Node class and create linked list nodes
// Your code here

Hint

Define a Node class with name and next fields. Create nodes and link them by setting next.

2

Set the search name

Create a string variable called searchName and set it to "Bob".

DSA C#

public class Node
{
    public string name;
    public Node next;

    public Node(string name)
    {
        this.name = name;
        this.next = null;
    }
}

Node head = new Node("Alice");
head.next = new Node("Bob");
head.next.next = new Node("Charlie");

// Create searchName variable and set it to "Bob"
// Your code here

Hint

Just create a string variable named searchName and assign it the value "Bob".

3

Search the linked list

Write a while loop to go through the linked list starting from head. Use a variable current to track the node. Inside the loop, check if current.name equals searchName. If yes, set a boolean variable found to true and break the loop. If the loop ends without finding, found should be false. Initialize found to false before the loop.

DSA C#

public class Node
{
    public string name;
    public Node next;

    public Node(string name)
    {
        this.name = name;
        this.next = null;
    }
}

Node head = new Node("Alice");
head.next = new Node("Bob");
head.next.next = new Node("Charlie");

string searchName = "Bob";

// Search the linked list for searchName
// Your code here

Hint

Use a while loop with a current node starting at head. Check each node's name. Set found to true and break if matched.

4

Print the search result

Write a Console.WriteLine statement that prints "Found" if found is true, otherwise prints "Not Found".

DSA C#

public class Node
{
    public string name;
    public Node next;

    public Node(string name)
    {
        this.name = name;
        this.next = null;
    }
}

Node head = new Node("Alice");
head.next = new Node("Bob");
head.next.next = new Node("Charlie");

string searchName = "Bob";

bool found = false;
Node current = head;
while (current != null)
{
    if (current.name == searchName)
    {
        found = true;
        break;
    }
    current = current.next;
}

// Print "Found" if found is true, else print "Not Found"
// Your code here

Hint

Use Console.WriteLine with an if statement to print "Found" or "Not Found" based on the found variable.

Practice

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

easy

A. To add a new node at the end

B. To find if the value exists in the list

C. To delete the first node

D. To reverse the linked 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 the value exists in the list -> Option B

4. Quick Check:

   Search = Find value presence [OK]

Hint: Search means checking nodes for the value [OK]

Common Mistakes:

• Confusing search with insertion or deletion
• Thinking search changes the list
• Assuming search returns the node position always

2. Which of the following is the correct C# syntax to start traversing a linked list from its head node named head?

easy

A. Node current => head;

B. Node current == head;

C. Node current = head;

D. Node current <- head;

Solution

1. Step 1: Understand variable assignment syntax in C#

   To assign a reference, use single equals sign =.

2. Step 2: Check each option for correct assignment

   Node current = head; uses =, which is correct. Others use invalid operators.

3. Final Answer:

   Node current = head; -> Option C

4. Quick Check:

   Assignment uses = in C# [OK]

Hint: Use single = for assignment in C# [OK]

Common Mistakes:

• Using == instead of = for assignment
• Using invalid operators like => or <-
• Confusing assignment with comparison

3. What will be the output of the following C# code snippet?

class Node {
  public int data;
  public Node next;
  public Node(int d) { data = d; next = null; }
}

Node head = new Node(5);
head.next = new Node(10);
head.next.next = new Node(15);

Node current = head;
bool found = false;
while (current != null) {
  if (current.data == 10) {
    found = true;
    break;
  }
  current = current.next;
}
Console.WriteLine(found);

medium

A. NullReferenceException

B. False

C. Compilation error

D. True

Solution

1. Step 1: Trace the linked list nodes and search loop

   The list has nodes with data 5 -> 10 -> 15. The loop checks each node's data for 10.

2. Step 2: Check when the value 10 is found

   At second node, data is 10, so found becomes true and loop breaks.

3. Final Answer:

   True -> Option D

4. Quick Check:

   Value 10 found = True [OK]

Hint: Stop loop when value found, print true [OK]

Common Mistakes:

• Forgetting to break loop after finding value
• Printing current.data instead of found
• Null pointer errors if next not checked

4. Identify the error in the following code that searches for a value in a linked list:

Node current = head;
while (current.next != null) {
  if (current.data == 20) {
    Console.WriteLine("Found");
    break;
  }
  current = current.next;
}

medium

A. It skips checking the last node

B. It causes infinite loop

C. It throws NullReferenceException immediately

D. It never enters the loop

Solution

1. Step 1: Analyze the loop condition

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

2. Step 2: Understand impact on search

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

3. Final Answer:

   It skips checking the last node -> Option A

4. Quick Check:

   Loop condition misses last node [OK]

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

Common Mistakes:

• Using current.next != null instead of current != null
• Assuming last node is checked automatically
• Not handling empty list (head null)

5. Given a linked list where nodes may contain duplicate values, how can you modify the search to return the count of occurrences of a target value x instead of just checking presence?

hard

A. Traverse all nodes, increment count when node.data == x, then return count

B. Stop at first occurrence and return 1

C. Use recursion to find only the last occurrence

D. Delete nodes with value x and return total nodes left

Solution

1. Step 1: Understand the need to count all occurrences

   Since duplicates exist, we must check every node to count all matches.

2. Step 2: Traverse entire list and count matches

   Loop through each node, increment a counter when node.data equals x, then return the count.

3. Final Answer:

   Traverse all nodes, increment count when node.data == x, then return count -> Option A

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
• Using recursion incorrectly for counting
• Modifying list during search unintentionally