Linked List vs Array When to Choose Which in DSA C# - Build Both Approaches

Linked List vs Array: When to Choose Which

📖 Scenario: Imagine you are managing a playlist of songs on your music app. You want to understand when to use an array or a linked list to store your songs efficiently.

🎯 Goal: You will create a simple playlist using an array and a linked list, then learn how to add songs and decide which data structure is better for different tasks.

📋 What You'll Learn

Create an array of strings called songArray with 3 songs

Create a linked list of strings called songList and add 3 songs

Add a new song to the end of songArray by creating a new array with one extra slot

Add a new song to the end of songList using linked list methods

Print both songArray and songList to compare

💡 Why This Matters

🌍 Real World

Music apps, photo galleries, and contact lists often choose between arrays and linked lists to store items efficiently.

💼 Career

Understanding when to use arrays or linked lists helps software developers write faster and more memory-efficient programs.

1

Create an array of songs

Create a string array called songArray with these exact songs: "SongA", "SongB", "SongC"

DSA C#

# Create the array 'songArray' with 3 songs
# Your code here

Hint

Use new string[] { ... } to create the array with the songs.

2

Create a linked list of songs

Create a LinkedList<string> called songList and add these exact songs in order: "SongA", "SongB", "SongC"

DSA C#

string[] songArray = new string[] { "SongA", "SongB", "SongC" };
// Create the linked list 'songList' and add 3 songs
// Your code here

Hint

Use new LinkedList<string>() to create the list and AddLast() to add songs.

3

Add a new song to the array and linked list

Add a new song "SongD" to the end of songArray by creating a new array with one extra slot and copying old songs. Then add "SongD" to the end of songList using AddLast.

DSA C#

using System.Collections.Generic;

string[] songArray = new string[] { "SongA", "SongB", "SongC" };
LinkedList songList = new LinkedList();
songList.AddLast("SongA");
songList.AddLast("SongB");
songList.AddLast("SongC");

// Add "SongD" to the end of songArray by creating a new array
// Add "SongD" to the end of songList
// Your code here

Hint

Arrays have fixed size, so create a new bigger array and copy old songs. LinkedList can add directly with AddLast.

4

Print both song collections

Print all songs in songArray separated by commas. Then print all songs in songList separated by commas.

DSA C#

using System.Collections.Generic;

string[] songArray = new string[] { "SongA", "SongB", "SongC" };
LinkedList songList = new LinkedList();
songList.AddLast("SongA");
songList.AddLast("SongB");
songList.AddLast("SongC");

string[] newSongArray = new string[songArray.Length + 1];
for (int i = 0; i < songArray.Length; i++)
{
    newSongArray[i] = songArray[i];
}
newSongArray[newSongArray.Length - 1] = "SongD";
songArray = newSongArray;

songList.AddLast("SongD");

// Print songs in songArray separated by commas
// Print songs in songList separated by commas
// Your code here

Hint

Use string.Join(", ", arrayOrList) to print all songs separated by commas.

Practice

1. Which data structure is better when you need fast random access to elements by index?

easy

A. Array

B. Linked List

C. Stack

D. Queue

Solution

1. Step 1: Understand random access in arrays

   Arrays store elements in contiguous memory, so accessing any element by index is fast and direct.

2. Step 2: Compare with linked list access

   Linked lists require traversal from the head to reach an element, making random access slower.

3. Final Answer:

   Array -> Option A

4. Quick Check:

   Fast random access = Array [OK]

Hint: For fast index access, choose Array [OK]

Common Mistakes:

• Thinking linked list supports fast random access
• Confusing stack or queue with random access
• Assuming linked list nodes are contiguous

2. Which of the following is the correct way to declare a linked list of integers in C#?

easy

A. List<int> list = new LinkedList<int>();

B. LinkedList<int> list = new LinkedList<int>();

C. LinkedList list = new List<int>();

D. List list = new LinkedList();

Solution

1. Step 1: Recall C# syntax for generic linked list

   The correct syntax uses LinkedList<T> with type parameter and new LinkedList<T>() to create an instance.

2. Step 2: Check each option for correctness

   LinkedList<int> list = new LinkedList<int>(); correctly declares and initializes a LinkedList<int>. Others mix types or omit generics.

3. Final Answer:

   LinkedList<int> list = new LinkedList<int>(); -> Option B

4. Quick Check:

   Correct generic linked list syntax = LinkedList<int> list = new LinkedList<int>(); [OK]

Hint: Use LinkedList<T> with new LinkedList<T>() [OK]

Common Mistakes:

• Mixing List and LinkedList types
• Omitting generic type parameter
• Using non-generic LinkedList without type

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

var list = new LinkedList<int>();
list.AddLast(10);
list.AddLast(20);
list.AddFirst(5);
foreach(var item in list) { Console.Write(item + " "); }

medium

A. 5 10 20

B. 10 20 5

C. 20 10 5

D. 5 20 10

Solution

1. Step 1: Trace linked list insertions

   First, 10 is added at the end, then 20 at the end, so list is [10, 20]. Then 5 is added at the front, making list [5, 10, 20].

2. Step 2: Output the list elements in order

   The foreach prints elements in order: 5, 10, 20 separated by spaces.

3. Final Answer:

   5 10 20 -> Option A

4. Quick Check:

   LinkedList order after AddFirst and AddLast = 5 10 20 [OK]

Hint: AddFirst puts element at start, AddLast at end [OK]

Common Mistakes:

• Assuming AddLast adds at front
• Confusing order of AddFirst and AddLast
• Forgetting foreach prints in list order

4. Identify the error in this code snippet that tries to add an element at index 2 in a linked list:

var list = new LinkedList<int>();
list.AddLast(1);
list.AddLast(2);
list.AddLast(3);
list.Add(2, 99);

medium

A. AddLast requires index parameter

B. AddLast cannot be called multiple times

C. List must be initialized with size

D. LinkedList does not have Add method with index parameter

Solution

1. Step 1: Check LinkedList methods in C#

   LinkedList<T> does not support Add with index; it only supports AddFirst, AddLast, or AddBefore/After nodes.

2. Step 2: Understand why Add(2, 99) causes error

   Calling Add with two parameters is invalid for LinkedList; this method exists in List<T> but not LinkedList.

3. Final Answer:

   LinkedList does not have Add method with index parameter -> Option D

4. Quick Check:

   LinkedList Add with index = invalid [OK]

Hint: LinkedList uses AddFirst/AddLast, no index Add [OK]

Common Mistakes:

• Using List methods on LinkedList
• Assuming Add can take index in LinkedList
• Confusing List<T> and LinkedList<T> APIs

5. You need to frequently insert and delete elements in the middle of a large collection. Which data structure is more efficient and why?

hard

A. Array, because it uses less memory

B. Array, because it allows fast random access

C. Linked List, because it allows fast insertions and deletions without shifting elements

D. Linked List, because it stores elements contiguously

Solution

1. Step 1: Analyze insertion and deletion in arrays

   Arrays require shifting elements after insertion or deletion in the middle, which is slow for large collections.

2. Step 2: Analyze linked list behavior

   Linked lists can insert or delete nodes by changing pointers without shifting, making these operations faster in the middle.

3. Final Answer:

   Linked List, because it allows fast insertions and deletions without shifting elements -> Option C

4. Quick Check:

   Fast middle insert/delete = Linked List [OK]

Hint: For frequent middle changes, choose Linked List [OK]

Common Mistakes:

• Choosing array for fast middle insert/delete
• Thinking linked list stores elements contiguously
• Ignoring cost of shifting in arrays