Array rotation is when you move array items by a defined number of places.
Let's say that we have an array of integers [1, 2, 3, 4, 5]that we need to rotate by 2 places in order to get an array [3, 4, 5, 1, 2] .

So, what did we do here?
If we do it by just swapping places, our logic would look like this:

Maybe you could use the above code to rotate small arrays, but please don’t use it as a solution.

If we apply more thinking into this then we can apply some logic and avoid nested loops and reduce the number of operations needed to rotate an array.

Algorithm:

1. Split array into two parts, first part is items from index 0 to the numberOfRotatitons-1.
2. Reverse first array
3. Reverse second array
4. Reverse whole array

This looks like an easy solution, now let's explain it with the real data.

We have an array [1, 2, 3, 4, 5],  and we need to rotate it by 2 places. Our first array will be from index 0 to index 1 (including value at the index 1) [1, 2], and second array will be from index 2 to index 4 [3, 4, 5].

Reversing first array [1, 2] we would get [2, 1].
Reversing second array [3, 4, 5] we would get [5, 4, 3]

Result of our work till now is an array [2, 1, 5, 4, 3]

Now we apply forth step of our algorithm and reverse whole array [2, 1, 5, 4, 3] into [3, 4, 5, 1, 2].

How do we convert this into the code?

In order to put this algorithm into the C# code, I will create two functions, one function will be logic for rotation, and the second function will be logic for reversing an array.

Let’s explain the code above:

If we have an array [1, 2] and we need to reverse that array then we need to swap values from index 1 to index 0. In order to save value from index 0, we need to put it into a tempvariable so we can later assign this value to the index 1 of our array.

array [1, 2]
temp = array[0] = 1
array[0] = array[1] = 2
array[1] = temp = 1
and we get an array [1, 2]

Now we have an array that looks like this [2, 1, 3, 4, 5] and we need to reverse second part so we will call our method ReverseArray(arr, 2, arr.Length-1)

and now we have an array that looks like [2, 1, 5, 4, 3] , and if we reverse it from start to the end ReverseArray(arr, 0, arr.Length-1) we will get an array that looks like [3, 4, 5, 1, 2]

In order to put this code in use, we need to create another function which will execute all those ReverseArray calls.

EXTRA

If you are asking your self where to put this code I will explain in details how you can create a new console project and put this into the code.

Step 1:

If you don’t have dotnet core you can get it at the URL https://dotnet.microsoft.com/download

Download SDK and runtime so you can run and build applications.

Step 2:

If you don’t have an IDE (Integrated Development Environment) you can download Visual Studio Code for free from this link: https://code.visualstudio.com/download

Step 3:

In your terminal/console/powershell (whatever pleases you) create a folder for this test e.g. RotatingArrays

Now, when everything is created you can create a project by typing into the console dotnet new console

Now you should be able to start Visual Studio Code by just typing code . into your console.

If everything is OK, you will see Visual Studio Code with the project that we created:

Now, we can put our code inside it and our code should look like

In order to see results of our work you can simply start a terminal inside Visual Studio Code, or use your own and write a command dotnet run and your application will be compiled and then started.