Write a program to rotate an array.

Question: Write a program to rotate an array arr[], having a size ‘n’ by ‘d’ elements?

Input: arr[] = { 4, 8, 15, 16, 23, 42, 99 }, d = 3
Output: 16, 23, 42, 99, 4, 8, 15

Let us suppose our array is in this way:

On rotating the array by 3 elements, it should look like:

To solve the above problem, we can adopt this following technique-

• Create a function that rotates the entire array by one element at a time.
• To rotate by one, store arr[0] in a temporary variable temp, move arr[1] to arr[0], arr[2] to arr[1] …and finally temp to arr[n-1]
• Create a function rotate(arr[], d, n) that calls the above function ‘d’ number of times.

Here is an implementation of the above algorithm:-

#include<stdio.h>

//function to rotate the array by one element
void leftRotatebyOne(int arr[], int n)
{
	int i, temp;
	temp = arr[0];

	//swap all the elements
	for (i = 0; i < n-1; i++)
		arr[i] = arr[i+1];

	arr[i] = temp;
}

/*Function to left rotate arr[] of size n by d*/
void leftRotate(int arr[], int d, int n)
{
	int i;

	//call the function to rotate by 1, d number of times
	for (i = 0; i < d; i++)
		leftRotatebyOne(arr, n);
}

//utility function to print an array
void printArray(int arr[], int size)
{
	int i;
	for(i = 0; i < size; i++)
		printf("%d ", arr[i]);
}

//Driver program to test above functions
int main(void)
{
	int arr[] = {4, 8, 15, 16, 23, 42, 99};

	leftRotate(arr, 3, 7);
	printArray(arr, 7);

	return 0;
}

Time Complexity: O(n * d)
Space Complexity: O(1)

Click here for method 2.