Task

An array A consisting of N integers is given. Rotation of the array means that each element is shifted right by one index, and the last element of the array is moved to the first place. For example, the rotation of array A = [3, 8, 9, 7, 6] is [6, 3, 8, 9, 7] (elements are shifted right by one index and 6 is moved to the first place).

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

Assume that the following declarations are given:

struct Results {
  int * A;
  int N; // Length of the array
};

Write a function:

    struct Results solution(int A[], int N, int K);  //prototype

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]

Given

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

the function should return [1, 2, 3, 4]

Assume that:

        N and K are integers within the range [0..100];
        each element of array A is an integer within the range [−1,000..1,000].

In your solution, focus on correctness. The performance of your solution will not be the focus of the assessment.

Brute Force Approach

The brute force approach is to shift each element in the array one place to the right, and the last element to the first place, for each pass, through the array. The brute force approach is accepted for this particular test, CyclicRotation; and it is used below. A struct with an integer sequence called, A is returned instead of an array, in the following program. The code, which the reader should read through, is:

    #include <stdio.h> 

    struct Results {
        int * A;
        int N; // Length of the array
    } stroct;
    
    struct Results solution(int A[], int N, int K) {
        stroct.A = &A[0];    //stroct.A and A[] now point to the same address;
        stroct.N = N;

        for(int i=0; i<K; i++) {
            if (N > 0) {
                int temp = A[N-1];
                //shift right by 1 index
                for (int j=N-1; j>0; j--) {    //end at j == 1
                    A[j] = A[j-1];
                }
                A[0] = temp;  //put last value in 1st place
            }
        }

        return stroct;
    }
  
    int main() 
    { 
        int N = 5;
        int B[] = {3, 8, 9, 7, 6};
        int K=3;
        struct Results str = solution(B, N, K);
        for (int i=0; i < str.N; ++i)
            printf("%i ", str.A[i]);

        return 0; 
    }

Note: Since the C function cannot return an array, a struct (Results str) with an integer sequence called A, is retuned instead.

The output is: 9 7 6 3 8, as expected. Read through the code, if that is not already done.

At app.codility.com/programmers, the score for correctness is 100%, for this function. Note that at app.codility.com, the main() C function is not typed (not sent to the server). At app.codility.com/programmers there is a score out of 100% for correctness, and also a score out of 100% for performance (reduced time complexity). Some middle value is taken as the total task score, still out of 100%. For this particular task, no mark is given for performance.

The reader should register at app.codility.com/programmers to be testing his/her own code.

That is it, for the explanation of this task.