LinkedList usage in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of LinkedList AddFirst and AddLast

What is the output of the following C# code?

C Sharp (C#)

using System;
using System.Collections.Generic;

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

A 10 5 20

B 20 10 5

C 10 20 5

D 5 10 20

💡 Hint

Remember AddFirst adds to the start, AddLast adds to the end.

AddFirst(10) puts 10 at start. AddLast(20) adds 20 at end. AddFirst(5) adds 5 at start, so list is 5, 10, 20.

❓ Predict Output

intermediate

LinkedList Remove and Count

What is the output of this C# code snippet?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        LinkedList<string> names = new LinkedList<string>();
        names.AddLast("Anna");
        names.AddLast("Bob");
        names.AddLast("Cara");
        names.Remove("Bob");
        Console.WriteLine(names.Count);
    }
}

A 2

B 1

C 0

D 3

💡 Hint

Removing an element decreases the count by one.

Initially 3 elements. Removing "Bob" leaves 2 elements: "Anna" and "Cara".

🔧 Debug

advanced

Find the error in LinkedList node insertion

What error will this C# code produce when run?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        LinkedList<int> numbers = new LinkedList<int>();
        numbers.AddLast(1);
        numbers.AddLast(3);
        var node = numbers.Find(2);
        numbers.AddAfter(node, 2);
        foreach (var n in numbers) {
            Console.Write(n + " ");
        }
    }
}

A NullReferenceException

B InvalidOperationException

C No error, output: 1 3 2

D ArgumentNullException

💡 Hint

Check what happens if Find returns null and you use it as a node.

Find(2) returns null because 2 is not in list. AddAfter(null, 2) throws NullReferenceException because node is null.

❓ Predict Output

advanced

LinkedList Reverse Traversal Output

What is the output of this C# code?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        LinkedList<char> letters = new LinkedList<char>();
        letters.AddLast('a');
        letters.AddLast('b');
        letters.AddLast('c');
        var node = letters.Last;
        while (node != null) {
            Console.Write(node.Value);
            node = node.Previous;
        }
    }
}

A abc

B cba

C bac

D cab

💡 Hint

Start from the last node and move backwards.

Starting at 'c' (last), then 'b', then 'a', prints 'cba'.

🧠 Conceptual

expert

LinkedList Node Removal Impact

Given a LinkedList with elements 1, 2, 3, 4, 5, what is the value of the node after removing the node with value 3?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        LinkedList<int> list = new LinkedList<int>(new int[] {1, 2, 3, 4, 5});
        var node = list.Find(3);
        var nextNode = node.Next;
        list.Remove(node);
        Console.WriteLine(nextNode.Value);
    }
}

A 3

B 5

C 4

D Throws InvalidOperationException

💡 Hint

Check what happens to the Next property of a node after removal.

nextNode points to node with value 4 before removal. Removing node 3 does not change nextNode reference. So nextNode.Value is 4.