POJ 2299

#include<iostream>
#include<stdio.h>
#define MAXN 500000  
using namespace std;

int a[MAXN];
int c[MAXN];
long long n;
void Merge(int le, int mid, int rh);
void MergeSort(int le, int rh);
int main()
{
    //freopen("acm.acm","r",stdin);
    int num;
    int i;
    while(cin>>num && num)
    {
        n = 0;
        for(i = 0; i < num; ++ i)
            cin>>a[i];
        MergeSort(0,num-1);
        //for(i = 0; i < num; ++ i)
        //    cout<<a[i]<<" ";
        //cout<<endl;
        cout<<n<<endl;
    }
}

void MergeSort(int le, int rh){
  
     
     if (rh>le)
     {
         int mid = (le+rh) >> 1;
         MergeSort(le,mid);
         MergeSort(mid + 1,rh);
         Merge(le, mid, rh);
     }
 }
 
 void Merge(int le, int mid, int rh)
 {
         int i, j,p = 1;
         for (i = le, j = mid+1; i <= mid && j <= rh; ) 
         {
             if (a[j] < a[i])
             {
                 c[p++] = a[j++];
                 n += mid - i + 1;    
             }
             else   c[p++] = a[i++];
         }
        while ( j <= rh )
                 c[p++] = a[j++];
        while( i <= mid )  
                 c[p++] = a[i++];
 
         for (i = le; i <= rh; ++i)        
         {
             a[i] = c[i - le + 1];
         }
 }