Consider n = 5. Naming the array elements as a1,a2,a3,a4,a5 , the final
required sum would be 4C0 * a5 - 4C1 * a4 + 4C2 * a3 - 4C3 * a2 + a1.

That is nothing but the pattern of a binomial expansion. Using this method,
the complexity can be reduced to O(n).

Correct me if I'm wrong!

On Tue, Apr 9, 2013 at 1:51 PM, Shashwat Kumar <shashwatkmr....@gmail.com>wrote:

> Recursion and iteration don't differ in this algorithm. But avoid using
> recursion if same can be done using iteration. In practical cases, system
> does not allow very large depth in recursion. So for large values of n,
> there can occur segmentation fault.
>
>
> On Tue, Apr 9, 2013 at 11:43 AM, rahul sharma <rahul23111...@gmail.com>wrote:
>
>> If you have any other solution ..please post that...i thnik recursion is
>> ok with base case...we need to scan again after first iteration...??
>>
>>
>> On Wed, Apr 10, 2013 at 12:12 AM, rahul sharma 
>> <rahul23111...@gmail.com>wrote:
>>
>>> i forgot to add base case..can add wen 2 elemnts are there then there
>>> sum is stored and we reurn from there...i m in hurry,,,sry for that,,
>>>
>>>
>>> On Wed, Apr 10, 2013 at 12:11 AM, Don <dondod...@gmail.com> wrote:
>>>
>>>> It is O(N^2) because the inner loop takes N steps to execute and that
>>>> loop will be executed N times.
>>>>
>>>> However, I would suggest not using recursion. There is no reason to
>>>> not do it iteratively. Your recursive solution has no base case so it
>>>> will recurse until your computer runs out of stack space, at which
>>>> point it will crash.
>>>>
>>>> Don
>>>>
>>>> On Apr 9, 2:29 pm, rahul sharma <rahul23111...@gmail.com> wrote:
>>>> >  A = {5, 3, 8, 9, 16}
>>>> > After one iteration A = {3-5,8-3,9-8,16-9}={-2,5,1,7}
>>>> > After second iteration A = {5-(-2),1-5,7-1} sum =7+(-4)+6=9
>>>> > Given an array, return sum after n iterations
>>>> >
>>>> > my sol/
>>>> > void abc(int arr[],n)
>>>> > {
>>>> > for(i=0;i<n;i++)
>>>> > arr[i]=arr[i+1]-arr[i];
>>>> > abc(arr,n-1);
>>>> >
>>>> > }
>>>> >
>>>> > I wana ask that the complexity is o(n) or o(n)2......as loop is
>>>> executed n
>>>> > times..say n is 10...so fxn is called 10 times....i.e  10 n..and
>>>> ignoring n
>>>> > it comes out to be...n......but if we implemeted with 2 loops then
>>>> > complexity is n2 ...and both sol are taking same no of
>>>> iterations...please
>>>> > tell whether complexity is n or n2 for above code....if it is n2 then
>>>> how???
>>>>
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>>>
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>
>
>
> --
> Shashwat Kumar
> Third year Undergraduate student
> Department of Computer Science and Engineering
> IIT Kharagpur
>
>
>
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-- 
Regards,
Shachindra A C

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