Array cutting and merging in C#

Question

I am trying to optimize a snake like game made in C# where I have an ArrayList that contains all the snake body parts stored. I need to be able to cut this ArrayList like if it was a deck of cards, where I would take the top part of the deck and make it the bottom one. This should help clarify.

01234 => 01 234 => 234 01 => 23401

This ArrayList can be as big as 300 elements and I need to make this operation as cheap as possible since this game is for mobile devices.

Answer 1

Using Array.Copy should be the fastest way to get there. But it requires you to use T[] array, not ArrayList.

public void CutTop<T>(this T[] source, int nbOfItemsToCut) {
    if(source == null)
        throw new ArgumentNullException("source");

    var length = source.Length;
    if(nbOfItemsToCut > length)
        throw new ArgumentException("nbOfItemsToCut");

    var temp = new T[nbOfItemsToCut];
    Array.Copy(source, temp, nbOfItemsToCut);

    Array.Copy(source, nbOfItemsToCut, source, 0, length - nbOfItemsToCut);
    Array.Copy(temp, 0, source, length - nbOfItemsToCut, nbOfItemsToCut);
}

Answer 2

Since you want to move items from beginning to end, a LinkedList<T> might be a good choice here, assuming you don't frequently access random elements within the list:

public void MoveToEnd<T>(LinkedList<T> list, int count)
{
    if(list == null)
        throw new ArgumentNullException("list");
    if(count < 0 || count > list.Count)
        throw new ArgumentOutOfRangeException("count");

    for (int i = 0; i < count; ++i)
    {
        list.AddLast(list.First.Value);
        list.RemoveFirst();
    }
}

var snake = new[] { 0, 1, 2, 3, 4 };
var list = new LinkedList<int>(snake);
Console.WriteLine(string.Join(" ", list)); // 0 1 2 3 4
MoveToEnd(list, 2);
Console.WriteLine(string.Join(" ", list)); // 2 3 4 0 1

In any case, I would suggest you measure the time it takes to perform this operation in your current implementation to see if it's actually necessary to optimize this part.