# Javascript Program for Block swap algorithm for array rotation

• Last Updated : 25 May, 2022

Write a function rotate(ar[], d, n) that rotates arr[] of size n by d elements.

Rotation of the above array by 2 will make array

Algorithm :

```Initialize A = arr[0..d-1] and B = arr[d..n-1]
1) Do following until size of A is equal to size of B

a)  If A is shorter, divide B into Bl and Br such that Br is of same
length as A. Swap A and Br to change ABlBr into BrBlA. Now A
is at its final place, so recur on pieces of B.

b)  If A is longer, divide A into Al and Ar such that Al is of same
length as B Swap Al and B to change AlArB into BArAl. Now B
is at its final place, so recur on pieces of A.

2)  Finally when A and B are of equal size, block swap them.```

Recursive Implementation:

## Javascript

 ``

Output:

`3 5 4 6 7 1 2`

Time Complexity: O(N), where N represents the size of the given array.
Auxiliary Space: O(N), due to recursive stack space.

Iterative Implementation:
Here is iterative implementation of the same algorithm. Same utility function swap() is used here.

## Javascript

 ``

Time Complexity: O(N), where N represents the size of the given array.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please see following posts for other methods of array rotation:
https://www.geeksforgeeks.org/array-rotation/
https://www.geeksforgeeks.org/program-for-array-rotation-continued-reversal-algorithm/

References:
http://www.cs.bell-labs.com/cm/cs/pearls/s02b.pdf
Please write comments if you find any bug in the above programs/algorithms or want to share any additional information about the block swap algorithm.

Please refer complete article on Block swap algorithm for array rotation for more details!

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