Search for a Value in Linked List in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a linked list?

A linked list is a chain of nodes where each node holds data and a link to the next node. It is like a treasure hunt where each clue leads to the next one.

beginner

How do you search for a value in a linked list?

Start at the first node and check its value. If it matches, stop. If not, move to the next node. Repeat until you find the value or reach the end.

beginner

What happens if the value is not found in the linked list?

You reach the end of the list (null) without finding the value. This means the value is not in the list.

intermediate

Why is searching in a linked list slower than in an array?

Because you must check nodes one by one from the start. Unlike arrays, linked lists do not allow jumping directly to the middle.

beginner

Show the JavaScript code snippet to search a value in a singly linked list.

function searchLinkedList(head, target) {
  let current = head;
  while (current !== null) {
    if (current.value === target) {
      return true;
    }
    current = current.next;
  }
  return false;
}

What does each node in a linked list contain?

A Data and a link to the next node

B Only data

C Only a link to the next node

D Data and a link to the previous node only

Each node holds data and a link to the next node, forming the chain.

What is the first step to search for a value in a linked list?

A Jump to the middle node

B Start from the last node

C Start from the first node

D Sort the list first

Searching starts from the first node and moves forward.

If the value is not found in the linked list, what will the search function return?

A True

B False

C Null

D The last node

The function returns false if the value is not found.

Why can't you jump directly to the middle of a linked list like in an array?

A Because nodes only link to the next node, no direct access

B Because linked lists are unordered

C Because linked lists are sorted

D Because arrays are slower

Linked lists have no direct access; you must follow links node by node.

What is the time complexity of searching a value in a linked list?

A O(1)

B O(log n)

C O(n^2)

D O(n)

Searching requires checking nodes one by one, so it is O(n).

Explain how to search for a value in a singly linked list step-by-step.

Think of walking through a chain of people asking for a name.

Write a simple JavaScript function to check if a value exists in a linked list.

Use a while loop and check current node's value.

Practice

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

easy

A. To find if the value exists in the list

B. To add a new node at the end

C. To delete the first node

D. To reverse the linked list

Solution

1. Step 1: Understand the search operation

   Searching in a linked list 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 list, not to modify the list.

3. Final Answer:

   To find if the value exists in the list -> Option A

4. Quick Check:

   Search means find value presence = C [OK]

Hint: Search means check nodes for value presence [OK]

Common Mistakes:

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

2. Which of the following is the correct way to start searching a linked list in JavaScript if head is the first node?

easy

A. let current = null;

B. let current = head;

C. let current = head.next.next;

D. let current = head.value;

Solution

1. Step 1: Understand the starting point of search

   Search starts from the first node, so we assign the first node to a variable to traverse.

2. Step 2: Choose the correct assignment

   Assigning head to current lets us start from the first node and move forward.

3. Final Answer:

   let current = head; -> Option B

4. Quick Check:

   Start search at head node = B [OK]

Hint: Start search at head node with let current = head [OK]

Common Mistakes:

• Starting at null means no nodes to check
• Skipping nodes by starting at head.next.next
• Assigning value instead of node reference

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

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

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

function search(head, target) {
  let current = head;
  while (current !== null) {
    if (current.value === target) {
      return true;
    }
    current = current.next;
  }
  return false;
}

console.log(search(head, 10));
console.log(search(head, 20));

medium

A. true\ntrue

B. false\ntrue

C. true\nfalse

D. false\nfalse

Solution

1. Step 1: Trace search for value 10

   Nodes are 5 -> 10 -> 15. The search finds 10 in the second node and returns true.

2. Step 2: Trace search for value 20

   20 is not in the list, so the loop ends and returns false.

3. Final Answer:

   true\nfalse -> Option C

4. Quick Check:

   10 found = true, 20 not found = false [OK]

Hint: Return true if found, else false after full traversal [OK]

Common Mistakes:

• Returning false too early
• Not updating current to next node
• Confusing value with node reference

4. Identify the error in the following search function for a linked list:

function search(head, target) {
  let current = head;
  while (current.next !== null) {
    if (current.value === target) {
      return true;
    }
    current = current.next;
  }
  return false;
}

medium

A. It does not check the last node's value

B. It uses incorrect variable names

C. It returns true too early

D. It never updates current

Solution

1. Step 1: Analyze the loop condition

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

2. Step 2: Check if last node is checked

   The last node's value is never checked because loop ends early, so search may miss target at last node.

3. Final Answer:

   It does not check the last node's value -> Option A

4. Quick Check:

   Loop misses last node check = D [OK]

Hint: Loop until current is null, not current.next [OK]

Common Mistakes:

• Using current.next !== null instead of current !== null
• Forgetting to check last node
• Assuming loop covers all nodes

5. Given a linked list where each node contains a number, how would you modify the search function to return the position (1-based) of the first occurrence of a target value, or -1 if not found?

hard

A. Reverse the list before searching for the value

B. Return true if value found; else false

C. Count total nodes first; then search for value

D. Initialize a position counter at 1; traverse nodes; return position if value matches; else -1

Solution

1. Step 1: Add a position counter starting at 1

   Initialize a variable to track the current node's position as you traverse the list.

2. Step 2: Traverse and compare values

   For each node, check if its value matches the target. If yes, return the current position.

3. Step 3: Return -1 if not found

   If traversal ends without finding the target, return -1 to indicate absence.

4. Final Answer:

   Initialize a position counter at 1; traverse nodes; return position if value matches; else -1 -> Option D

5. Quick Check:

   Position tracking with traversal = A [OK]

Hint: Track position while searching; return position or -1 [OK]

Common Mistakes:

• Returning boolean instead of position
• Not updating position counter
• Reversing list unnecessarily