Codility CyclicRotation – Python Solution

This post is a Python solution to the Codility CyclicRotation problem (Lesson 2 – Arrays) which scored 100%. Now, Let’s understand the problem first.

CyclicRotation Problem:

Rotate an array to the right by a given number of steps.

Although the problem is described quite elaborately at Codility, here is just an outline with an example.

In this problem, there are 2 input parameters:

1. A – an array consisting of N integers. Each element of array A is an integer within the range [−1,000..1,000].
2. K – each element of A will be shifted to the right K times. K is an integer within the range [0..100];

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

Example:

A = [3, 8, 9, 7, 6]

K = 3

Expected Output: [9, 7, 6, 3, 8]

Python Solution:

If we check the above-expected output, although we are supposed to rotate the array 3 times like below, what we are actually doing is splitting the array at the Kth position and refitting it.

[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]

We will use K = K % n, where n is the total number of elements in the array. For this example, K = 3. Thus, we will return A[-3:] + A[:-3]

A = [3, 8, 9, 7, 6]
A[-3:] + A[:-3]

Let’s take another example:

A = [1, 2, 3, 4] & K = 4

[1, 2, 3, 4] -> [4, 1, 2, 3]

[4, 1, 2, 3] -> [3, 4, 1, 2]

[3, 4, 1, 2] -> [2, 3, 4, 1]

[2, 3, 4, 1] -> [1, 2, 3, 4]

Now, for this example total elements in the array (n) = 4 and even K = 4. Thus, K = 4 % 4 = 0.

Now, splitting at position 0 which got the same output as the array.

Code:

Test Cases:

A = [3, 8, 9, 7, 6]
K = 3
result = solution(A,K)
print(result)

The function returned : [9, 7, 6, 3, 8]

A = [1, 2, 3, 4]
K = 4
result = solution(A,K)
print(result)

The function returned :[1, 2, 3, 4]

A = [0, 0, 0]
K = 1
result = solution(A,K)
print(result)

The Function returned: [0, 0, 0]

Conclusion:

Codility runs the solution for different test cases which are extremes and create a report with Test Results on Correctness and Performance. For this particular problem, Performance is not assessed.

For this problem, I have tried to write loops and rotate elements one by one and that works too. But the above solution looks most simple.

Please leave a comment if the solution did not work for you. Or, Clap once if you think the post is helpful.

Check for more solutions for codility problem:

Codility BinaryGap – Python Solution

Thank You!

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