How to rotate an array to the right by K steps

Given an array of integers and k, return a rotated array to the right by k steps

Example 1

Input:    array = [1, 2, 3, 4], k = 1

Output:   [4, 1, 2, 3]

Example 2

Input:    array = [1, 2, 3, 4], k = 0

Output:   [1, 2, 3, 4]

Algorithm

First of all, we need to answer the question. What does it meat to rotate an array to the right n k steps?

To rotate an array on k steps we need to move each element on k steps to the right other words each element's index should be incremented on k.

Let's see an example step by step

 

 

k is equal to two, each element's index should be incremented by two. It can be done by two steps, on each step, an index will be incremented by one.

 

 

It's easy for indexes: 0, 1, 2. What should we do for 3, 4, and 5? After incremented by 2 an index will be out of the array bounds. To solve it we can use the euclidean division and count a new index by formula:

(i + k) % array.Length. where i is an element's index in the array

Calculation of a new index:

(0 + 2) % 5 = 2
(1 + 2) % 5 = 3
(2 + 2) % 5 = 4
(3 + 2) % 5 = 0
(4 + 2) % 5 = 1

Code

    public int[] Rotate(int[] array, int k)
    {
        if (array == null || array.Length == 0 || k == 0)
        {
            return array;
        }

        var result = new int[array.Length];

        for (int i = 0; i < array.Length; i++)
        {
            result[(i + k) % array.Length] = array[i];
        }

        return result;
    }

Time Complexity: O(n)