UVA 10810 Ultra Quicksort Solution

Problem Statement
Difficulty : Easy.
Problem Type : Sorting(Merge Sort).  

Solution : It is a counting inversion problem which can be solved using merge sort. See UVA 11495 Bubbles and Buckets Solution To get the idea to solve this problem.
Here,is the C implementation of the problem.

#include <stdio.h>

#define sz 500000
#define inf 1000000000
long a[sz+2],cnt,L[sz+2],R[sz+2];

void merge(long p,long q,long r){
 long i,j,k,ind1,ind2;

 for(i = p,ind1 = 1;i <= q;i++){
  L[ind1++] = a[i];
 }
 L[ind1] = inf;

 for(i = q+1,ind2 = 1;i <= r;i++){
  R[ind2++] = a[i];
 }
 R[ind2] = inf;

 i = j = 1;

 for(k = p;k <= r;k++){
  if(L[i] > R[j]){
   cnt += ind1 - i;
   a[k] = R[j];
   j++;
  }
  else{
   a[k] = L[i];
   i++;
  }
 }
}

void mergeSort(long p,long r){
 if(p < r){
  long q = (p+r)/2;
  mergeSort(p,q);
  mergeSort(q+1,r);
  merge(p,q,r);
 }
}

int main(){
 long i,n;

 while(scanf("%ld",&n)&&n){
  for(i = 1;i <= n; i++){
   scanf("%ld",&a[i]);
  }
  cnt = 0;
  mergeSort(1,n);
  printf("%ld\n",cnt);
 }

 return 0;
}