Personalized sorting algorithm that operates on just half of the array. (in C) - arrays

Question

I have a simple task but I found myself running in circles.
I need to "create" a sorting algorithm using already seen classic ones that will sort an array using the lowest possible number of memory accesses.
The generated array has some rules though:
the first half is generated like this A[i]=rand() % (n/10);, so we have small numbers spanning from 0 to 9.
the second half is like that A[i]=(n-i)*(n-i);, here we have bigger numbers, but they're generated in a descending order.
For the first half I found that using counting sort is very effective, giving me around 4.5k memory accesses. For the second half, the best way is to just reverse the array since it's already decreasing, but I do want it in an ascending order.
My idea was splitting the array in two sub arrays, sorting the first one, reversing the second one and then merging and printing them.
I wrote a split function:
void split(int* A, int* A1, int* A2, int q){
for(int i=0; i<q; i++){
A1[i]=A[i];
ct_op=ct_op+2; //ci perdo un 10k accessi
}
for(int i=q+1; i<q*2-1; i++){
A2[i]=A[i];
ct_op=ct_op+2;
}} //where q is the dim of the array /2
Then I apply the counting sort to my array A1 that works and gives me back my B array which is now ordered. Now, I can't seem to reverse the second half of the array (which should be contained in A2).
void reverse(int* A, int dim){
int i; int j; int temp;
for(i=n/2, j=n-1; i<j; i++,j--){
temp=A[i];
A[i]=A[j];
A[j]=temp;
}}
That doesn't work and the array doesn't get reversed.
Another problem that I have is that the A2 array doesn't start from the half of the A1 array. It's just a bunch (array dim/2) of 0s and then I get the second half of the arrays:
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2500 2401 2304 2209 2116 2025 1936 1849 1764 1681 1600 1521 1444 1369 1296 1225 1156 1089 1024 961 900 841 784 729 676 625 576 529 484 441 400 361 324 289 256 225 196 169 144 121 100 81 64 49 36 25 16 0 0
why is that? I could just start printing from half of it, but that's not quite what I'm looking for.
I guess the TLDR is how do I properly split an array and how do I reverse the content of it?
Thank you.

Answer 1

I' ll just use the variables from your code and try to answer the TLDR, because your code is very inefficient.
The following picture shows the array A (which is just a pointer), the pointer A1 and the pointer A2.
As you can see here there is no need for splitting it with the for-loops you used. You just call your count sort algorithm with the pointer A or A1 and the length q and you pass the pointer A2 and the length q to a array reverse algorithm.
I found some implementations for such an array reverse algorithm here.