CyclicRotation at app.codility.com in C Plus Plus Explained - Rotate an array to the right by a given number of steps.
Foreword: Category of Article - Technology, Computers and Software, Algorithm
By: Chrysanthus Date Published: 21 Jan 2024
Task
Lesson 2 at app.codility.com/programmers
The solution and its explanation are given below.
Problem
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.
Write a function:
vector<int> solution(vector<int> &A, 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. A vector is used instead of an array, in the following program. The code, which the reader should read through, is:
#include <iostream>
#include <vector>
using namespace std;
vector<int> solution(vector<int> &A, int K) {
int N = A.size();
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--) {
A[j] = A[j-1];
}
A[0] = temp; //put last in 1st place
}
}
return A;
}
int main()
{
vector<int> B({3, 8, 9, 7, 6});
vector<int> C();
int K=3;
vector<int> V = solution(B, K);
for (int i=0; i<V.size(); ++i)
cout << V[i] <<' ';
cout << endl;
return 0;
}
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 (small 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.