- Write a program to rotate an array using
**block swap algorithm**. - Array rotation Block swap algorithm implementation.

Given an integer array of size N we have to rotate it by K elements without using any extra memory space.

For Example :

Input Array : 1 2 3 4 5 6 7 8 K = 3 Output : 4 5 6 7 8 1 2 3

Let inputArray be an integer array of size N.

**Array Rotation Block Swap Algorithm**

- Split inputArray into two sub Array X and Y, where X is from index 0 to K-1 and Y is from index K to N-1.
- If X is smaller than Y
- Split Y into YLeft and YRight such that size of YRight is equal to size of X. inputArray will be X|YLeft|YRight.
- Swap X and YRIght. Now, inputArray will look like YRight|Yleft|X. X is now in correct position.
- Recursively block swap YRight and YLeft.

- If Y is smaller than X
- Split X into XLeft and XRight such that size of XLeft is equal to size of Y. inputArray will be XLeft|XRight|Y.
- Swap Y and XLeft. Now, inputArray will look like Y|XRight|XLeft. Y is now in correct position.
- Recursively block swap XRight and XLeft.

- If size of X is equal to size of Y, then swap X and Y.

## C program to rotate an array using block swap algorithm.

#include <stdio.h> /* This function swaps two sub arrays of length L, starting from left and right index */ void swapArraySegment(int *array, int left, int right, int L){ int i, temp; for(i = 0; i < L; i++) { /* swapping array element at index left+i and right+i */ temp = array[left + i]; array[left + i] = array[right + i]; array[right + i] = temp; } } void rotateArray(int *array, int N, int size) { /* Input Validation */ if(array == NULL || size == 0 || N == 0 || N == size) return; /* If elements to be rotated is equal to first half of the given array */ if(size - N == N){ /* swap left and right half of array */ swapArraySegment(array, 0, size-N, N); return; } /* If X(left Segment) is smaller than Y */ if(N < size-N) { /* Swap X and Y_right */ swapArraySegment(array, 0, size-N, N); /* Recursively swap remaining elements */ rotateArray(array, N, size-N); } else { /* If Y(right Segment) is smaller than X */ swapArraySegment(array, 0, N, size-N); rotateArray(array+size-N, 2*N-size, N); } } int main(){ int array[10] = {0,1,2,3,4,5,6,7,8,9}; int i; printf("Original Array\n"); for(i = 0; i<10; i++){ printf("%d ", array[i]); } rotateArray(array, 4, 10); printf("\nRotated Array\n"); for(i = 0; i<10; i++){ printf("%d ", array[i]); } return 0; }Output

Original Array 0 1 2 3 4 5 6 7 8 9 Rotated Array 4 5 6 7 8 9 0 1 2 3