Rotate Array

 Given an unsorted array arr[] of size N. Rotate the array to the left (counter-clockwise direction) by D steps, where D is a positive integer. 

Example 1:

Input:
N = 5, D = 2
arr[] = {1,2,3,4,5}
Output: 3 4 5 1 2
Explanation: 1 2 3 4 5  when rotated
by 2 elements, it becomes 3 4 5 1 2.

Example 2:

Input:
N = 10, D = 3
arr[] = {2,4,6,8,10,12,14,16,18,20}
Output: 8 10 12 14 16 18 20 2 4 6
Explanation: 2 4 6 8 10 12 14 16 18 20 
when rotated by 3 elements, it becomes 
8 10 12 14 16 18 20 2 4 6.

Your Task:
Complete the function rotateArr() which takes the array, D and N as input parameters and rotates the array by D elements. The array must be modified in-place without using extra space. 
 
Expected Time Complexity: O(N)
Expected Auxiliary Space: O(1)
 
Constraints:
1 <= N <= 107
1 <= D <= N
0 <= arr[i] <= 105


Solution
// { Driver Code Starts
#include<bits/stdc++.h>
using namespace std;


 // } Driver Code Ends
class Solution{
    public:
    
    void reverse(int arr[],int low,int high){
        while(low<high){
            swap(arr[low],arr[high]);
            low++;
            high--;
        }
    }
    //Function to rotate an array by d elements in counter-clockwise direction. 
    void rotateArr(int arr[], int d, int n){
        // code here
        reverse(arr,0,d-1);
        reverse(arr,d,n-1);
        reverse(arr,0,n-1);
    }
};

// { Driver Code Starts.

int main() {
	int t;
	//taking testcases
	cin >> t;
	
	while(t--){
	    int n, d;
	    
	    //input n and d
	    cin >> n >> d;
	    
	    int arr[n];
	    
	    //inserting elements in the array
	    for(int i = 0; i < n; i++){
	        cin >> arr[i];
	    }
	    Solution ob;
	    //calling rotateArr() function
	    ob.rotateArr(arr, d,n);
	    
	    //printing the elements of the array
	    for(int i =0;i<n;i++){
	        cout << arr[i] << " ";
	    }
	    cout << endl;
	}
	return 0;
}  // } Driver Code Endsn: