Traversal and Printing a Linked List in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start traversal from the head of the linked list.

DSA Javascript

let current = [1];

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

Ahead

Btail

Cnext

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tail' instead of 'head' to start traversal.

Assigning 'null' which means no node.

The traversal of a linked list starts from the head node.

2fill in blank

medium

Complete the code to move to the next node in the linked list during traversal.

DSA Javascript

current = current.[1];

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

Anext

Btail

Cprev

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists.

Using 'head' or 'tail' which are not properties of a node.

To move forward in a singly linked list, you use the next pointer.

3fill in blank

hard

Fix the error in the while loop condition to correctly traverse until the end of the linked list.

DSA Javascript

while (current [1] null) {
  console.log(current.value);
  current = current.next;
}

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

A>

B==

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment '=' instead of comparison.

Using '==' which may cause issues with type coercion.

Using '>' which is not valid for object comparison.

The loop should continue while current is not null, so use !=.

4fill in blank

hard

Fill both blanks to create a function that prints all values in the linked list.

DSA Javascript

function printList([1]) {
  let current = [2];
  while (current != null) {
    console.log(current.value);
    current = current.next;
  }
}

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

Ahead

Bnode

CheadNode

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for parameter and traversal start.

Using undefined variables inside the function.

The function parameter and the starting point for traversal should be the same node, here named headNode.

5fill in blank

hard

Fill all three blanks to create a function that returns a string representation of the linked list values separated by ' -> '.

DSA Javascript

function listToString([1]) {
  let current = [2];
  let result = '';
  while (current != null) {
    result += current.value;
    if (current.next != null) {
      result += [3];
    }
    current = current.next;
  }
  return result;
}

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

AheadNode

C' -> '

D' ->'

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for parameter and traversal start.

Missing spaces in the separator string.

Adding separator after the last node.

The function parameter and traversal start are headNode. The separator string is ' -> ' with spaces around the arrow.

Practice

1. What does it mean to traverse a linked list?

easy

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

B. To delete the first node of the list

C. To visit each node in the list one by one from start to end

D. To reverse the order of nodes in the list

Solution

1. Step 1: Understand traversal meaning

   Traversal means going through each element in a data structure in order.

2. Step 2: Apply to linked list

   For a linked list, traversal means visiting each node from the first to the last.

3. Final Answer:

   To visit each node in the list one by one from start to end -> Option C

4. Quick Check:

   Traversal = Visit nodes in order [OK]

Hint: Traversal means visiting nodes one by one [OK]

Common Mistakes:

• Confusing traversal with insertion or deletion
• Thinking traversal changes the list order
• Assuming traversal skips nodes

2. Which of the following is the correct way to start traversing a singly linked list in JavaScript?

easy

A. let current = head;

B. let current = tail;

C. let current = null;

D. let current = head.next.next;

Solution

1. Step 1: Identify the start of the list

   The traversal starts from the first node, called head.

2. Step 2: Assign current pointer

   Setting current = head means we start visiting from the first node.

3. Final Answer:

   let current = head; -> Option A

4. Quick Check:

   Start traversal at head [OK]

Hint: Traversal always starts at head node [OK]

Common Mistakes:

• Starting at tail which is the last node
• Starting at null which means no node
• Skipping nodes by starting at head.next.next

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(1);
head.next = new Node(2);
head.next.next = new Node(3);

let current = head;
let result = '';
while (current !== null) {
  result += current.value + ' -> ';
  current = current.next;
}
result += 'null';
console.log(result);

medium

A. null -> 1 -> 2 -> 3

B. 1 -> 2 -> 3 -> null

C. 1 -> 2 -> 3

D. 3 -> 2 -> 1 -> null

Solution

1. Step 1: Trace the linked list nodes

   The list has nodes with values 1, 2, and 3 linked in order.

2. Step 2: Follow the while loop

   The loop appends each node's value followed by ' -> ' until current is null, then adds 'null'.

3. Final Answer:

   1 -> 2 -> 3 -> null -> Option B

4. Quick Check:

   Print nodes in order with arrow and null [OK]

Hint: Follow each node and append value with arrow [OK]

Common Mistakes:

• Forgetting to add 'null' at the end
• Printing nodes in reverse order
• Missing arrows between nodes

4. The following code is intended to print all values in a linked list. What is the error?

let current = head;
while (current.next !== null) {
  console.log(current.value);
  current = current.next;
}

medium

A. It will print undefined values

B. It will cause an infinite loop

C. It will throw a syntax error

D. It will skip printing the last node's value

Solution

1. Step 1: Analyze the loop condition

   The loop runs while current.next is not null, so it stops before last node.

2. Step 2: Check which nodes get printed

   It prints current.value inside loop, so last node (where current.next is null) is not printed.

3. Final Answer:

   It will skip printing the last node's value -> Option D

4. Quick Check:

   Loop condition excludes last node [OK]

Hint: Use current !== null to include last node [OK]

Common Mistakes:

• Using current.next !== null instead of current !== null
• Assuming last node is printed
• Confusing loop condition with syntax error

5. You want to print a linked list in reverse order without modifying the list or using extra arrays. Which approach is best?

hard

A. Use recursion to traverse to the end, then print on return

B. Traverse normally and print values as you go

C. Reverse the list first, then print

D. Use a loop with current.next !== null condition

Solution

1. Step 1: Understand the problem constraints

   We cannot modify the list or use extra arrays, so reversing or storing values is not allowed.

2. Step 2: Use recursion to print in reverse

   Recursion goes to the end of the list, then prints values on the way back, achieving reverse order without extra storage.

3. Final Answer:

   Use recursion to traverse to the end, then print on return -> Option A

4. Quick Check:

   Recursion prints reverse without extra space [OK]

Hint: Recursion prints reverse by returning from end [OK]

Common Mistakes:

• Trying to reverse list which modifies it
• Using loops that print forward only
• Using extra arrays which is disallowed