C# LinkedList vs List: Comparing Performance and Use Cases

In C#, both LinkedList<T> and List<T> are commonly used collection types that serve different purposes and have distinct performance implications depending on their use. Understanding the differences between these two can help developers choose the most appropriate type based on their specific needs. This article explores the fundamental differences, advantages, and disadvantages of using LinkedList<T> versus List<T> in C#.

Understanding List<T> and LinkedList<T>

List<T> is a generic collection that is backed by an array and provides fast index-based access to elements. It is similar to an array but can dynamically resize as needed.

LinkedList<T> is a doubly linked list implementation that allows each element to be linked to both the previous and next elements. This structure enables efficient insertion and deletion operations.

Key Differences Between List<T> and LinkedList<T>

Memory Allocation

List<T>: Internally uses an array to store the elements. When the array needs to grow, it creates a new array and copies the elements to the new array, which can be costly for large lists.
LinkedList<T>: Each element (node) contains three parts: the value, a reference to the next node, and a reference to the previous node. This means that it requires more memory per element than List<T>, but it can be more efficient for inserting and deleting elements.

Performance Considerations

Access: List<T> provides fast, direct access to elements via an index, making it suitable for scenarios where such access is frequent. LinkedList<T>, lacking direct access, requires traversal from the start or the end to reach an element, which can be time-consuming.
Insertions and Deletions:
- List<T>: Efficient at the end of the list but can be inefficient in the middle or at the start because it requires shifting elements.
- LinkedList<T>: Offers constant time insertion and deletion at any point in the list, provided you have a reference to the node before or after which you want to insert or remove.

Use Cases

List<T>: Ideal for applications where quick retrieval of elements is necessary and modifications to the collection are infrequent or primarily occur at the end of the collection.
LinkedList<T>: More suitable for scenarios where the collection is frequently modified by inserting or removing elements, especially when these operations can occur at various points in the collection.

Code Examples

Using List<T>:

List<int> numbers = new List<int>();
numbers.Add(1);  // Adding elements at the end is efficient
numbers.Insert(0, 0);  // Inserting at the beginning requires shifting all elements
Console.WriteLine(numbers[0]);  // Fast access

Using LinkedList<T>:

LinkedList<int> numbers = new LinkedList<int>();
var firstNode = numbers.AddFirst(1);  // Efficient
numbers.AddBefore(firstNode, 0);  // Also efficient if you have the node reference
// To access elements, you need to traverse the list
for (var node = numbers.First; node != null; node = node.Next)
{
    Console.WriteLine(node.Value);
}

Conclusion

The choice between using List<T> and LinkedList<T> should be based on specific application needs. If indexed access is required and list modifications are minimal, List<T> is likely the better choice. However, if the application involves frequent insertions and deletions from various parts of the collection, LinkedList<T> might be more appropriate due to its efficient dynamic operations.

c# linked list vs list