LinkedList usage in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new LinkedList of integers.

C Sharp (C#)

LinkedList<int> numbers = new LinkedList<int>[1];

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

A()

B[]

C{}

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets instead of parentheses.

Using curly braces which are for collection initializers.

Using angle brackets which are for generics.

The correct syntax to create a new LinkedList is to use parentheses () after the type.

2fill in blank

medium

Complete the code to add the value 10 at the end of the LinkedList.

C Sharp (C#)

numbers.[1](10);

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

AAddLast

BAddAfter

CAddFirst

DAddBefore

Attempts:

3 left

💡 Hint

Common Mistakes

Using AddFirst which adds at the start.

Using AddAfter or AddBefore without a reference node.

Use AddLast to add a new element at the end of the LinkedList.

3fill in blank

hard

Fix the error in the code to remove the first element from the LinkedList.

C Sharp (C#)

numbers.[1]();

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

ADeleteFirst

BRemoveLast

CRemoveAt

DRemoveFirst

Attempts:

3 left

💡 Hint

Common Mistakes

Using RemoveLast which removes the last element.

Using RemoveAt which does not exist for LinkedList.

Using DeleteFirst which is not a valid method.

The method RemoveFirst() removes the first element from the LinkedList.

4fill in blank

hard

Fill both blanks to check if the LinkedList contains the value 5 and then add it if not present.

C Sharp (C#)

if (!numbers.[1](5)) {
    numbers.[2](5);
}

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

AContains

BAddLast

CAddFirst

DRemove

Attempts:

3 left

💡 Hint

Common Mistakes

Using Remove instead of Contains for checking.

Adding with AddFirst instead of AddLast.

Use Contains to check if the value exists, and AddLast to add it at the end if not.

5fill in blank

hard

Fill all three blanks to create a LinkedList of strings, add "hello" at the start, and then remove "world".

C Sharp (C#)

LinkedList<string> words = new LinkedList<string>[1];
words.[2]("hello");
words.[3]("world");

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

A()

BAddFirst

CRemove

DAddLast

Attempts:

3 left

💡 Hint

Common Mistakes

Using AddLast instead of AddFirst for adding "hello".

Using RemoveFirst or RemoveLast instead of Remove with a value.

Create the LinkedList with (), add "hello" at the start with AddFirst, and remove "world" with Remove.

Practice

1. What is a key characteristic of a LinkedList in C#?

easy

A. It stores elements in nodes linked by references.

B. It stores elements in a fixed-size array.

C. It only allows adding elements at the end.

D. It cannot remove elements once added.

Solution

1. Step 1: Understand LinkedList structure

   A LinkedList stores elements in nodes, where each node points to the next (and possibly previous) node.

2. Step 2: Compare options with LinkedList behavior

   Only It stores elements in nodes linked by references. correctly describes this linked node structure; others describe arrays or incorrect behaviors.

3. Final Answer:

   It stores elements in nodes linked by references. -> Option A

4. Quick Check:

   LinkedList = nodes linked by references [OK]

Hint: LinkedList uses nodes connected by links, not arrays. [OK]

Common Mistakes:

• Thinking LinkedList uses arrays internally
• Assuming LinkedList only adds at the end
• Believing LinkedList cannot remove elements

2. Which of the following is the correct way to add an element at the start of a LinkedList<int> named list?

easy

A. list.AddStart(10);

B. list.AddFirst(10);

C. list.InsertAt(0, 10);

D. list.PushFront(10);

Solution

1. Step 1: Recall LinkedList method names

   The method to add an element at the start is AddFirst.

2. Step 2: Check each option's validity

   Only AddFirst is a valid LinkedList method; others are invalid or do not exist.

3. Final Answer:

   list.AddFirst(10); -> Option B

4. Quick Check:

   AddFirst adds at start [OK]

Hint: Use AddFirst to add at the start of LinkedList. [OK]

Common Mistakes:

• Using non-existent methods like AddStart or PushFront
• Confusing LinkedList with List methods
• Trying to use InsertAt which LinkedList does not have

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

var list = new LinkedList<string>();
list.AddLast("apple");
list.AddFirst("banana");
list.AddLast("cherry");
foreach(var item in list) Console.Write(item + " ");

medium

A. banana apple cherry

B. apple banana cherry

C. cherry apple banana

D. banana cherry apple

Solution

1. Step 1: Track insertion order

   First, "apple" is added last, so list: apple. Then "banana" added first, so list: banana, apple. Then "cherry" added last, so list: banana, apple, cherry.

2. Step 2: Understand foreach iteration order

   Foreach iterates from first to last node, so output is "banana apple cherry ".

3. Final Answer:

   banana apple cherry -> Option A

4. Quick Check:

   First = banana, last = cherry [OK]

Hint: AddFirst puts item at start; AddLast at end. [OK]

Common Mistakes:

• Assuming AddLast adds at start
• Confusing order of AddFirst and AddLast
• Expecting output in reverse order

4. Identify the error in this code snippet:

var list = new LinkedList<int>();
list.AddFirst(1);
list.AddLast(2);
list.Remove(3);
Console.WriteLine(list.Count);

medium

A. Remove(3) throws an exception because 3 is not in the list.

B. Count property does not exist on LinkedList.

C. AddFirst and AddLast methods are invalid for LinkedList.

D. Remove(3) does nothing since 3 is not found; Count remains 2.

Solution

1. Step 1: Understand Remove behavior

   Remove(value) tries to remove the first node with that value. If not found, it does nothing and returns false; no exception is thrown.

2. Step 2: Check Count after removal attempt

   Since 3 is not in the list, list remains with 2 elements; Count is 2.

3. Final Answer:

   Remove(3) does nothing since 3 is not found; Count remains 2. -> Option D

4. Quick Check:

   Remove missing value = no error, Count unchanged [OK]

Hint: Remove missing item does not throw error, just returns false. [OK]

Common Mistakes:

• Expecting Remove to throw exception if item missing
• Thinking AddFirst/AddLast are invalid
• Assuming Count is not a property

5. Given a LinkedList<int> with values 1, 2, 3, 4, 5, which code snippet correctly removes all even numbers from the list?

hard

A. foreach(var node in list) { if(node % 2 == 0) list.Remove(node); }

B. for(int i = 0; i < list.Count; i++) { if(list.ElementAt(i) % 2 == 0) list.Remove(list.ElementAt(i)); }

C. var current = list.First; while(current != null) { var next = current.Next; if(current.Value % 2 == 0) list.Remove(current); current = next; }

D. list.RemoveAll(x => x % 2 == 0);

Solution

1. Step 1: Understand safe removal during iteration

   Removing nodes while iterating requires storing next node before removal to avoid invalid references.

2. Step 2: Analyze each option

   foreach(var node in list) { if(node % 2 == 0) list.Remove(node); } uses foreach which throws error on modification during iteration. var current = list.First; while(current != null) { var next = current.Next; if(current.Value % 2 == 0) list.Remove(current); current = next; } correctly uses a while loop with next node saved. for(int i = 0; i < list.Count; i++) { if(list.ElementAt(i) % 2 == 0) list.Remove(list.ElementAt(i)); } uses ElementAt which is inefficient and unsafe. list.RemoveAll(x => x % 2 == 0); is invalid as LinkedList has no RemoveAll method.

3. Final Answer:

   var current = list.First; while(current != null) { var next = current.Next; if(current.Value % 2 == 0) list.Remove(current); current = next; } -> Option C

4. Quick Check:

   Use while loop with next saved to remove nodes safely [OK]

Hint: Save next node before removal to avoid iteration errors. [OK]

Common Mistakes:

• Modifying list inside foreach causes runtime error
• Using RemoveAll which LinkedList does not have
• Using ElementAt which is inefficient and unsafe