Question

Given my current extension method:

public static List<char> rotate(this List<char> currentList, int periodes) {
    if (periodes != 1) {
        int x = currentList.Count() - 1;
        return rotate(currentList.Skip(x).
             Concat(currentList.Take(x)).ToList<char>(), periodes - 1);
    }
    return currentList;
}

Original State:

ring = new List<char>() { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j' };

Current Result for ring.rotate(10);

J A B C D E F G H I
I J A B C D E F G H
H I J A B C D E F G
G H I J A B C D E F
F G H I J A B C D E      Recursive Steps
E F G H I J A B C D
D E F G H I J A B C
C D E F G H I J A B
B C D E F G H I J A

---

A B C D E F G H I J      Result

Is there any way to get rid of this while loop and any chance to integrate the repetition into the LINQ query?

Best
Henrik

Answer 1

Skip i and concat i

public static class Ex
{
    public static List<char> Rotate(this List<char> c, int i)
    {
        i %= c.Count;
        return c.Skip(i).Concat(c.Take(i)).ToList();
    }
}

class Program
{
    static void Main()
    {
        List<char> chars = new List<char>();

        for (int i = 65; i < 75; ++i)
        {
            chars.Add((char)i);
        }

        var r1 = chars.Rotate(10); // A B C D E F G H I J
        var r2 = chars.Rotate(1); // B C D E F G H I J A
        var r3 = chars.Rotate(101); // B C D E F G H I J A
        var r4 = chars.Rotate(102); // C D E F G H I J A B

        Console.ReadLine();
    }
}