c# Adding a Remove(int index) method to the .NET Queue class

Question

I would like to use the generic queue class as described in the .NET framework (3.5) but I will need a Remove(int index) method to remove items from the queue. Can I achieve

Answer 1

I do not believe we should be using List to emulate a queue, for a queue, the enqueue and dequeue operations should be very highly performant, which they would not be when using a List. For the RemoveAt method however, it is acceptable to be non-performant, as it is not the primary purpose of a Queue.

My approach at implementing RemoveAt is O(n) but the queue still maintains a largely O(1) enqueue (sometimes the internal array needs reallocating which makes the operations O(n)) and always O(1) dequeue.

Here is my implementation of a RemoveAt(int) extension method for a Queue:

public static void RemoveAt(this Queue queue, int index)
{
    Contract.Requires(queue != null);
    Contract.Requires(index >= 0);
    Contract.Requires(index < queue.Count);

    var i = 0;

    // Move all the items before the one to remove to the back
    for (; i < index; ++i)
    {
        queue.MoveHeadToTail();
    }

    // Remove the item at the index
    queue.Dequeue();

    // Move all subsequent items to the tail end of the queue.
    var queueCount = queue.Count;
    for (; i < queueCount; ++i)
    {
        queue.MoveHeadToTail();
    }
}

Where MoveHeadToTail is defined as follows:

private static void MoveHeadToTail(this Queue queue)
{
    Contract.Requires(queue != null);

    var dequed = queue.Dequeue();
    queue.Enqueue(dequed);
}

This implementation also modifies the actual Queue rather than returning a new Queue (which I think is more in-keeping with other RemoveAt implementations).