arrays - Easiest way to Rotate a List in c#

Question

Lists say I have a list List<int> {1,2,3,4,5}

Rotate means:

=> {2,3,4,5,1} => {3,4,5,1,2} => {4,5,1,2,3}

Maybe rotate is not the best word for this, but hope you understand what I means

My question, whats the easiest way (in short code, c# 4 Linq ready), and will not be hit by performance (reasonable performance)

Thanks.

Answer 1

List<T>

The simplest way (for a List<T>) is to use:

int first = list[0];
list.RemoveAt(0);
list.Add(first);

Performance is nasty though - O(n).

Array

This is basically equivalent to the List<T> version, but more manual:

int first = array[0];
Array.Copy(array, 1, array, 0, array.Length - 1);
array[array.Length - 1] = first;

LinkedList<T>

If you could use a LinkedList<T> instead, that would be much simpler:

int first = linkedList.First;
linkedList.RemoveFirst();
linkedList.AddLast(first);

This is O(1) as each operation is constant time.

Queue<T>

cadrell0's solution of using a queue is a single statement, as Dequeue removes the element and returns it:

queue.Enqueue(queue.Dequeue());

While I can't find any documentation of the performance characteristic of this, I'd expect Queue<T> to be implemented using an array and an index as the "virtual starting point" - in which case this is another O(1) solution.

Note that in all of these cases you'd want to check for the list being empty first. (You could deem that to be an error, or a no-op.)