block-swap-array.cpp

//Program for bloack swap algorithm in an array
#include <bits/stdc++.h>
using namespace std;

/*functions Prototypes */
void printArray(int arr[], int size);
void swap(int arr[], int fi, int si, int d);

void leftRotate(int arr[], int d, int n)
{
	/* Return If number of elements to be rotated
	is zero or equal to array size */
	if(d == 0 || d == n)
		return;
	/* If number of elements to be rotated is more than array size*/
	if(d > n)
	d = d % n;
	/*If number of elements to be rotated
	is exactly half of array size */
	if(n - d == d)
	{
		swap(arr, 0, n - d, d);
		return;
	}
		
	/* If A is shorter*/	
	if(d < n - d)
	{
		swap(arr, 0, n - d, d);
		leftRotate(arr, d, n - d);	
	}
	else /* If B is shorter*/	
	{
		swap(arr, 0, d, n - d);
		leftRotate(arr + n - d, 2 * d - n, d); /*This is tricky*/
	}
}

/*UTILITY FUNCTIONS USED*/
/* function to print an array */
void printArray(int arr[], int size)
{
	int i;
	for(i = 0; i < size; i++)
		cout << arr[i] << " ";
	cout << endl;
}

/*This function swaps d elements starting at index fi
with d elements starting at index si */
void swap(int arr[], int fi, int si, int d)
{
	int i, temp;
	for(i = 0; i < d; i++)
	{
		temp = arr[fi + i];
		arr[fi + i] = arr[si + i];
		arr[si + i] = temp;
	}
}

// Driver Program
int main()
{
	int arr[] = {1, 2, 3, 4, 5, 6, 7};
	leftRotate(arr, 2, 7);
	printArray(arr, 7);
	return 0;
}

// Naveen Kumar Sahu