When should I use a List vs a LinkedList in C#?

When to Use a List vs a LinkedList in C#

In C#, List<T> and LinkedList<T> are two different types of collections that serve different purposes. Understanding their characteristics and differences can help you decide which one to use in various scenarios.

List<T>

List<T> is a generic collection provided by the .NET Framework, implemented as a dynamic array. It is part of the System.Collections.Generic namespace.

Characteristics

• Contiguous Memory Allocation: Elements are stored in contiguous memory locations, which allows for fast access by index.
• Index-Based Access: Provides O(1) time complexity for accessing elements by index.
• Efficient for Append Operations: Adding elements to the end of the list (using Add) is typically O(1) unless the list needs to be resized.
• Resizing: When the internal array is full, the list needs to be resized (usually doubling its capacity), which involves copying the elements to a new array.

When to Use List<T>

• Random Access: When you need fast, index-based access to elements.
• Append Operations: When you frequently add elements to the end of the list.
• Memory Efficiency: When you need a collection with lower memory overhead compared to LinkedList<T>.
• Common Use Cases: Storing collections of items where you often access elements by index, such as arrays, stacks, or queues.

Example

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };

        // Access element by index
        Console.WriteLine(numbers[2]); // Output: 3

        // Add an element
        numbers.Add(6);

        // Insert an element at a specific index
        numbers.Insert(2, 10);

        // Remove an element
        numbers.Remove(4);

        // Iterate over the list
        foreach (var number in numbers)
        {
            Console.WriteLine(number);
        }
    }
}

LinkedList<T>

LinkedList<T> is a generic doubly linked list provided by the .NET Framework, part of the System.Collections.Generic namespace.

Characteristics

• Nodes and References: Each element (node) contains a reference to the next and previous node, allowing for efficient insertions and deletions.
• No Index-Based Access: Does not support fast access by index. Accessing elements requires traversing the list.
• Efficient Insertions/Deletions: Insertions and deletions are O(1) operations if you already have a reference to the node.
• Memory Overhead: Higher memory overhead compared to List<T> due to additional references stored in each node.

When to Use LinkedList<T>

• Frequent Insertions/Deletions: When you need to frequently insert or delete elements, especially in the middle of the collection.
• No Index-Based Access Needed: When you do not require fast access by index.
• Complex Data Structures: When implementing complex data structures such as queues, stacks, or graph algorithms.

Example

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        LinkedList<int> numbers = new LinkedList<int>();

        // Add elements
        numbers.AddLast(1);
        numbers.AddLast(2);
        numbers.AddLast(3);

        // Insert element at the beginning
        numbers.AddFirst(0);

        // Insert element after a specific node
        LinkedListNode<int> node = numbers.Find(2);
        numbers.AddAfter(node, 2);

        // Remove an element
        numbers.Remove(3);

        // Iterate over the linked list
        foreach (var number in numbers)
        {
            Console.WriteLine(number);
        }
    }
}

Summary

• Use List<T> when:

  • You need fast, index-based access to elements.
  • You frequently append elements to the end of the list.
  • You want lower memory overhead.
  • You need a versatile, general-purpose collection.

• Use LinkedList<T> when:

  • You need to frequently insert or delete elements, especially in the middle of the collection.
  • You do not need fast, index-based access to elements.
  • You are implementing complex data structures or algorithms that benefit from efficient insertions and deletions.

Understanding these differences and choosing the appropriate collection type can lead to more efficient and readable code. For more in-depth knowledge and practical examples on collections and other programming concepts, consider exploring Grokking the Coding Interview on DesignGurus.io, which provides comprehensive courses on essential coding and interview techniques.