Search for a Value in Linked List in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start traversing the linked list from the head node.

DSA Javascript

function searchLinkedList(head, target) {
  let current = [1];
  while (current !== null) {
    if (current.value === target) {
      return true;
    }
    current = current.next;
  }
  return false;
}

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

Ahead

Btail

Cnull

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing current to 'tail' instead of 'head'.

Initializing current to 'null' which stops traversal immediately.

We start traversing the linked list from the head node, so 'current' should be initialized to 'head'.

2fill in blank

medium

Complete the condition to check if the current node's value matches the target.

DSA Javascript

if (current.[1] === target) {
  return true;
}

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

Atarget

Bvalue

Chead

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing current.next to target instead of current.value.

Using 'head' or 'target' as a property which does not exist on the node.

Each node stores its data in the 'value' property, so we compare current.value with the target.

3fill in blank

hard

Fix the error in updating the current node to the next node during traversal.

DSA Javascript

current = current.[1];

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

Avalue

Btarget

Chead

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning current to current.value which is data, not a node.

Assigning current to current.head which is undefined.

To move to the next node, we assign current to current.next.

4fill in blank

hard

Fill both blanks to complete the while loop condition and the return value when the target is not found.

DSA Javascript

while (current [1] null) {
  if (current.value === target) {
    return true;
  }
  current = current.next;
}
return [2];

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

A!==

B==

Cfalse

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!==' in the while condition.

Returning true when the target is not found.

The loop continues while current is not null, and if the target is not found, the function returns false.

5fill in blank

hard

Fill all three blanks to create a function that searches for a value in a linked list and returns true if found, false otherwise.

DSA Javascript

function searchList([1], target) {
  let current = [2];
  while (current !== null) {
    if (current.[3] === target) {
      return true;
    }
    current = current.next;
  }
  return false;
}

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

Ahead

Cvalue

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' as the parameter name instead of 'head'.

Comparing current.next to target instead of current.value.

The function takes 'head' as input, starts traversal from 'head', and compares 'current.value' to the target.

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