POJ 2299 Ultra-QuickSort

POJ 2299 Ultra-QuickSort

求逆序对个数。我是用离散化+树状数组做的。
以下是我的代码：

/*
 * Author:  lee1r
 * Created Time:  2011/8/5 23:33:01
 * File Name: poj2299.cpp
  */
#include < iostream >
#include < sstream >
#include < fstream >
#include < vector >
#include < list >
#include < deque >
#include < queue >
#include < stack >
#include < map >
#include < set >
#include < bitset >
#include < algorithm >
#include < cstdio >
#include < cstdlib >
#include < cstring >
#include < cctype >
#include < cmath >
#include < ctime >
#define  L(x) ((x)<<1)
#define  R(x) (((x)<<1)+1)
#define  Half(x) ((x)>>1)
#define  lowbit(x) ((x)&(-(x)))
using   namespace  std;
const   int  kInf( 0x7f7f7f7f );
const   double  kEps(1e - 8 );
typedef  long   long  int64;
typedef unsigned  long   long  uint64;

const   int  kMaxn( 500007 );

struct  Type
{
     int  id,value,num;
};

bool  cmp1( const  Type  & a, const  Type  & b)
{
     return  a.value < b.value;
}

bool  cmp2( const  Type  & a, const  Type  & b)
{
     return  a.id < b.id;
}

int  n,bit[kMaxn];
Type r[kMaxn];
int64 ans;

void  Add( int  x, int  delta)
{
     for ( int  i = x;i <= n;i += lowbit(i))
        bit[i] += delta;
}

int  Sum( int  x)
{
     int  re( 0 );
     for ( int  i = x;i > 0 ;i -= lowbit(i))
        re += bit[i];
     return  re;
}

int  main()
{
     // freopen("data.in","r",stdin);
    
     while (scanf( " %d " , & n) == 1   &&  n)
    {
         for ( int  i = 1 ;i <= n;i ++ )
        {
            scanf( " %d " , & r[i].value);
            r[i].id = i;
        }
        sort(r + 1 ,r + n + 1 ,cmp1);
         for ( int  i = 1 ;i <= n;i ++ )
            r[i].num = i;
        sort(r + 1 ,r + n + 1 ,cmp2);
        
        ans = 0 ;
        memset(bit, 0 , sizeof (bit));
         for ( int  i = 1 ;i <= n;i ++ )
        {
            Add(r[i].num, 1 );
            ans += i - Sum(r[i].num - 1 ) - 1 ;
        }
        
        cout << ans << endl;
    }
    
     return   0 ;
}