Arrays: Given an array and a number n, rotate the array by n steps to its right.

Example:
Array = {1, 2, 3, 4, 5 ,6, 7};
n = 4

Explanation:
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rotate 1 steps to the right: [7, 1, 2, 3, 4, 5, 6]
rotate 2 steps to the right: [6, 7, 1, 2, 3, 4, 5]
rotate 3 steps to the right: [5, 6, 7, 1, 2, 3, 4]
rotate 4 steps to the right: [4, 5, 6, 7, 1, 2, 3]

This problem can be solved in 2 different ways.

Method 1: Take the copy of the array and rotate the elements.

In this solution we take a copy of the array then, we replace the items based on the formula “(i + k)%len”.
This will start from the position to be rotated. Then copy the elements from the copy array to the original array.

Test Case:
K = 4, hence the position will become
i = 0 k = 4 len = 7 (i + k)%len = 4
i = 1 k = 4 len = 7 (i + k)%len = 5
i = 2 k = 4 len = 7 (i + k)%len = 6
i = 3 k = 4 len = 7 (i + k)%len = 0
i = 4 k = 4 len = 7 (i + k)%len = 1
i = 5 k = 4 len = 7 (i + k)%len = 2
i = 6 k = 4 len = 7 (i + k)%len = 3

Method 2: By reversing the array 3 times.

Reverse 1: Reverse the whole array
Reverse 2: Reverse the elements from 0 to k.
Reverse 3: Reverse from k to n.

Solution in C++

#include<iostream>
#include<vector>

using namespace std;


vector<int> rotate_method_1(vector<int> array, int k) 
{
    int len = array.size();
    //take the copy of the array
    vector<int> array_copy(len);
    for (int i = 0; i < len; i++)
    {
        array_copy[i] = array[i];
    }
    
    // Rotate the elements.
    for (int i = 0; i < len; i++)
    {
        array[(i + k)%len] = array_copy[i];
    }
    return array;
}

vector<int> rotate_method_2(vector<int> array, int k) 
{
    int len = array.size();
 
    reverse(array.begin(), array.end()); 
    reverse(array.begin(), array.begin()+k%len); 
    reverse(array.begin()+k%len, array.begin()+len); 


    return array;
}

int main()
{

    vector<int> array = {1, 2, 3, 4, 5, 6, 7};
    int k = 4;

    cout<<"Before Rotation "<<endl;

    for (int i = 0; i < array.size(); i++)
    {
        cout <<array[i] << " ";
    }

    cout<<"\n\nAfter Rotation using method 1:"<<endl;

    vector<int> result = rotate_method_1(array, k);

    for (int i = 0; i < result.size(); i++)
    {
        cout <<result[i] << " ";
    }
    cout<<endl;

    cout<<"\n\nAfter Rotation using method 2:"<<endl;

    result = rotate_method_2(array, k);

    for (int i = 0; i < result.size(); i++)
    {
        cout <<result[i] << " ";
    }
    cout<<endl;

    return 0;
}

Output:

Before Rotation
1 2 3 4 5 6 7

After Rotation using method 1:
4 5 6 7 1 2 3


After Rotation using method 2:
4 5 6 7 1 2 3