# Reversal algorithm

I know what is reversal algorithm and I know how it works. but I want to know why it works??
Can someone help me out??

I know what is Binary Search and I know how it works. But I want to know why it works??
Can you help me out??

binary search works because data is sorted and we are sure if the element to be searched is greater than a[mid] then ans will not be on the left side and vice versa.

If u don’t want to help, don’t help. I’m not here to listen to your lame answers.

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Okay, I would like to help you (seriously). Can you specify what exactly you mean by “Reversal Algorithm”.
String Reversal?
Array Reversal?
Or what?
And look how your question sounds.

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Array reversal. (It can also be applied to strings)

And sorry if I was not clear with my question.
I’m talking about the following algorithm.

https://www.geeksforgeeks.org/program-for-array-rotation-continued-reversal-algorithm/

``````Let an array R be composed of two subarrays A and B i.e. R=A+B

Let our reverse function be rev().

Then, rev(R)=rev(A+B)=rev(B)+rev(A) ---(1)

E.g. R=1,2,3,4,5,6,7. Let A=1,2,3 and B=4,5,6,7
Then rev(R)=7,6,5,4,3,2,1 viz. rev(B) + rev(A)

Now as per the question, let R be rotated d times.
Let A=R[1..d] and B=[d+1..n]

We go by the reversal algorithm. After reversal of A and B, R=rev(A)+rev(B)
Thus, applying equation (1), rev(R)=rev(rev(A)+rev(B))=rev(rev(B))+rev(rev(A))=B+A

Hence our array R gets rotated by the algo.

Note that this + is not the arithmetic one, but is used here to signify array concatenation i.e. A+B != B+A``````
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