HDU 2689 POJ 2299 树状数组 + 离散化

以前都是直接树状数组裸奔，昨天一个题数据量好大，过不了，没办法只能学离散化，今天A了第一个离散化的题

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define Max 500005
long long s,a[Max];
int n,max;
struct e
{
       int num,f;
}N[Max];
int cmp( const void *a,const void *b )
{
    return ( ( e * )a ) -> num - ( ( e * )b ) -> num;
}
inline int lowbit( int  x )
{
       return x & ( -x );
}
void update( int x )
{
     while( x <= max )
     {
            a[x]++;
            x += lowbit( x );
            }
 }
long long sum( int x )
{
    long long s = 0;
    while( x )
    {
           s += a[x];
           x -= lowbit( x );
           }
    return s;
}
int main(  )
{
    while( scanf( "%d",&n ) != EOF && n )
    {
           max = s = 0;
           memset( a,0,sizeof( a ) );
           for( int i = 1; i <= n; ++i )
           {
                scanf( "%d",&N[i].num );
                N[i].f = i;
            }
           qsort( N + 1,n,sizeof( N[1] ),cmp );
           max = n;
           for( int i = 0; i < n; ++i )
           {
                int x = N[i+1].f;
                s += i - sum( x );
                update( x );
            }
            printf( "%I64d\n",s );
           }
    return 0;
}