I'm learning C#, I programmed some things in java, and I would like to have a feedback on my C# code.
The exercise is from codility.

The goal is to rotate array A K times; that is, each element of A will be shifted to the right K times.

Write a function:

class Solution { public int[] solution(int[] A, int K); }

that, given an array A consisting of N integers and an integer K, returns the array A rotated K times.

For example, given

A = [3, 8, 9, 7, 6]
K = 3 the function should return [9, 7, 6, 3, 8]. Three rotations were made:

[3, 8, 9, 7, 6] -> [6, 3, 8, 9, 7]
[6, 3, 8, 9, 7] -> [7, 6, 3, 8, 9]
[7, 6, 3, 8, 9] -> [9, 7, 6, 3, 8] For another example, given

A = [0, 0, 0]
K = 1 the function should return [0, 0, 0]


A = [1, 2, 3, 4]
K = 4 the function should return [1, 2, 3, 4]

And this is my code. It gives 100% but maybe something can be improved.Thanks in advice.

using System;
// you can also use other imports, for example:
// using System.Collections.Generic;

// you can write to stdout for debugging purposes, e.g.
// Console.WriteLine("this is a debug message");

class Solution {
    public int[] solution(int[] A, int K) {
        int len = A.Length;
        int[] B = new int[len];
        if(len > 0 && K % len != 0 )
            for ( int i = 0; i < len; i++)
                B[(K + i) % len] = A[i];
            return A;
        return B;
  • \$\begingroup\$ Now that I'm looking at it, I believe B could be created inside the if... so if no cyclic rotation is needed computer could save the creation of a potentially large array \$\endgroup\$
    – newbie
    Sep 20, 2019 at 12:34

1 Answer 1


Good Practices

  • ✔ I like the fact you don't rotate if the array's length is a multiplication of K.
  • ✔ As you stated in the comments, the second array B gets created too early, since in some occasions it would be created in vain.


  • The challenge is clearly written for Java:class Solution { public int[] solution(int[] A, int K); }. The provided signature deserves its own review (casing conventions, static members, meaningful member names). However, if you 'cannot' change the signature given to you, I would be consistent and use N instead of len for the array's length.
  • You sometimes return the provided array and sometimes create a new one. I would make this very clear in the specification. A consumer should know whether or when a copy is returned. This affects further usage of the object.
  • You should guard against the source array being null.
  • How would you handle a negative value of K? If you think about it, a left rotation is just the inverse of a right rotation.
  • Nested statements could have been prevented by inverting the if-statement and exiting early. Less nested statements generally increase readability.
  • For bigger arrays you should check Buffer.BlockCopy to optimize copying sections of an array to another array. You could see a rotation as copying 2 sections from one array to another given a pivot. Check out this article about the subject.
  • If you can change the signature, make a static class with static method, use a meaningful method name RotateRight with arguments array and count and make it clear whether in-place rotation is performed or a new array is created.

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