11858 - Frosh Week

#include <stdio.h>
#include <cstring>
#define max 1000009
int a[max] , L[max] , R[max];
long long int p = 0;
void merge (int a[] , int l ,int m , int r)
{
    int i , j , k;
    int n1 = m - l + 1 , n2 = r - m;
    for(i = 0; i < n1; i++)
    {
        L[i] = a[l + i];
    }
    for(j = 0; j < n2; j++)
    {
        R[j] = a[m + 1 + j];
    }
    i = 0;
    j = 0;
    k = l;
    int x = 0;
    while(i < n1 && j < n2)
    {
        if(L[i] <= R[j])
        {
            a[k] = L[i] , p += x;
            i++;
        }
        else
        {
            a[k] = R[j] , x++;
            j++;
        }
        k++;
    }
    while(i < n1)
    {
        a[k] = L[i] , p += x;
        i++;
        k++;
    }
    while(j < n2)
    {
        a[k] = R[j];
        j++;
        k++;
    }

}
void mergesort(int a[] , int l , int r)
{
    if(l < r)
    {
        int m = (l + r) / 2;

        mergesort(a ,l, m);
        mergesort(a, m + 1, r);
        merge(a , l , m , r);
    }
}
int main()
{
    int tes, i;
    while(scanf("%d", &tes) == 1)
    {
        for(i = 0; i < tes; i++)
        {
            scanf("%d", &a[i]);
        }
        p = 0;
        mergesort(a, 0, tes - 1);
       printf("%lld\n",p);
    }
}