Easiest way to Rotate a List in c#

Question

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

Rotate means:

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

Answer 1

List

The simplest way (for a List) 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 version, but more manual:

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

LinkedList

If you could use a LinkedList 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

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 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.)