Traversal and Printing a Linked List in DSA Typescript - Time & Space Complexity

Time Complexity: Traversal and Printing a Linked List

O(n)

Understanding Time Complexity

We want to understand how long it takes to go through a linked list and print its values.

The question is: how does the time needed change when the list gets bigger?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

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

function printList(head: Node | null): void {
  let current = head;
  while (current !== null) {
    console.log(current.value);
    current = current.next;
  }
}
    

This code goes through each node in the linked list and prints its value one by one.

Identify Repeating Operations

• Primary operation: The while loop that visits each node once.
• How many times: Exactly once per node, so as many times as there are nodes (n times).

How Execution Grows With Input

As the list gets longer, the number of steps grows directly with the number of nodes.

Input Size (n)	Approx. Operations
10	10 steps
100	100 steps
1000	1000 steps

Pattern observation: The time grows in a straight line with the number of nodes.

Final Time Complexity

Time Complexity: O(n)

This means the time to print the list grows directly with the number of nodes.

Common Mistake

[X] Wrong: "The printing takes constant time because it just prints values."

[OK] Correct: Each node must be visited and printed, so time grows with the list size, not fixed.

Interview Connect

Understanding this helps you explain how simple list operations scale, a key skill in many coding interviews.

Self-Check

"What if we changed the linked list to a doubly linked list? How would the time complexity of printing change?"

Practice

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

easy

A. Visit each node in the list one by one from start to end

B. Add a new node at the end of the list

C. Delete the first node of the list

D. Reverse the order of nodes in the list

Solution

1. Step 1: Understand traversal meaning

   Traversal means going through each element in order to access or process it.

2. Step 2: Apply to linked list context

   In a linked list, traversal means visiting each node starting from the head until the end (null).

3. Final Answer:

   Visit each node in the list one by one from start to end -> Option A

4. Quick Check:

   Traversal = Visit nodes sequentially [OK]

Hint: Traversal means visiting nodes one after another [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 linked list in TypeScript?

easy

A. let current = head;

B. let current = tail;

C. let current = null;

D. let current = new Node();

Solution

1. Step 1: Identify starting point for traversal

   Traversal starts from the first node, called head, to visit all nodes.

2. Step 2: Check options for correct initialization

   Setting current to head allows moving through nodes; tail or null won't start traversal properly.

3. Final Answer:

   let current = head; -> Option A

4. Quick Check:

   Start traversal at head node [OK]

Hint: Always start traversal from the head node [OK]

Common Mistakes:

• Starting traversal from tail which is the last node
• Initializing current to null which skips traversal
• Creating a new node instead of using existing head

3. What will be the output of the following TypeScript code that prints a linked list?

class Node {
  value: number;
  next: Node | null;
  constructor(value: number) {
    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;
while (current !== null) {
  console.log(current.value);
  current = current.next;
}

medium

A. 3 2 1

B. 1 2 3

C. 1 3 2

D. 2 3 1

Solution

1. Step 1: Understand list structure

   The list nodes are linked as 1 -> 2 -> 3 -> null.

2. Step 2: Trace the while loop output

   The loop prints current.value starting at head (1), then moves to 2, then 3, then stops at null.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Print nodes in order: 1 2 3 [OK]

Hint: Print values while moving from head to next until null [OK]

Common Mistakes:

• Printing in reverse order by mistake
• Skipping nodes by incorrect pointer update
• Confusing node values order

4. Identify the error in this linked list traversal code and select the fix:

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

medium

A. Remove console.log inside the loop

B. Add console.log after the loop

C. Initialize current to null

D. Change condition to current !== null

Solution

1. Step 1: Analyze loop condition

   The loop stops when current.next is null, so it skips printing the last node.

2. Step 2: Fix condition to include last node

   Changing condition to current !== null ensures all nodes, including last, are printed.

3. Final Answer:

   Change condition to current !== null -> Option D

4. Quick Check:

   Loop until current is null to print all nodes [OK]

Hint: Loop until current is null to include last node [OK]

Common Mistakes:

• Using current.next !== null misses last node
• Not updating current inside loop causes infinite loop
• Printing after loop instead of inside

5. Given a linked list with nodes containing values 5 -> 10 -> 15 -> null, write a TypeScript function to traverse and collect these values into an array. What will be the returned array after traversal?

hard

A. [15, 10, 5]

B. [5, 15, 10]

C. [5, 10, 15]

D. [10, 5, 15]

Solution

1. Step 1: Traverse from head to end

   Start at head (5), then move to 10, then 15, collecting values in order.

2. Step 2: Collect values in array during traversal

   Push each node's value into an array as you visit it, resulting in [5, 10, 15].

3. Final Answer:

   [5, 10, 15] -> Option C

4. Quick Check:

   Values collected in order visited [OK]

Hint: Collect values while traversing from head to null [OK]

Common Mistakes:

• Collecting values in reverse order
• Skipping nodes by wrong pointer update
• Returning array before traversal completes