Question

I’ve been searching for the standard implementation of a doubly linked list in c# (so that I have a linked list I can iterate over backwards) and cannot find one. I feel like something so simple must have an implementation that I’m just missing.

If it does exist, for which version of c#/.net does it exist?

Reverse iteration in general seems to be something not intended to be done in c#. Is my mind just stuck too much in c++/stl mode or is this something sorely lacking in c#?

I’m aware of LinkedList but in failing to find a way to iterate over it backwards had assumed it was singly linked.

If LinkedList is doubly linked how does one go about iterating over it backwards (Efficiently)?

Answer 1

As well as the answers given here, you can write an extension method to LinkedList<T> to make it slightly easier to reuse:

public static IEnumerable<T> Backwards<T>(this LinkedList<T> list)
{
    LinkedListNode<T> node= list.Last;
    while (node != null)
    {
        yield return node.Value;
        node = node.Previous;
    }
}

Use with:

foreach (string x in list.Backwards())
{
    // ...
}