7kyu problem, unless you know math formulae. Not a fan.

Please use spoiler flag next time, your post was visible in the homepage.

What do you need clarification about? First you sort the array in descending order, then you sum up the differences.

instructions it not clear about sorting stuff need more clarify explanation and some additional example

Can someone explain what kind of calculation this kata wants from me? Right now I 'am sorting the array in descending order, splitting the are in half so I get two arrays and then subtract from the first index until there is no more elements in the array in both arrays and then I add the arrays(Sum) together.

It seems I 'am missunderstanding the description.

Description will lead you into O(nlog(n)) solution at most.
It would be helpful to have in the description info that there is a neat O(n) math solution to the problem.

that's not a proper issue report

per the description your code must handle empty vectors and return 0 in that case; but your code crashes because in the loop

 for(;begin+1 != end;begin++){
        int a = *(begin);
// ...

you dereference an empty vector, which is undefined behavior.
Please ask questions to ask for help in the future, an issue is a provable flaw in the kata ;-)

CoffeeScript translation

pure fun

good kata, but instruction should be clearer regarding sorting

Sample tests for C and NASM have a minor bug, if you get the answer wrong for the array of length 0, you crash with a SIGSEGV. (At first I thought I may have messed up seriously somewhere lol).
This seems to be because you slip into an unwanted loop here:

while (--n) // RIP when n == 0
    pos += sprintf(s+pos, "%s%i", p, *a++);

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