HDU 2689 Sort it

HDU 2689 Sort it

序列中有多少个逆序对冒泡排序就需要多少次交换。
以下是我的代码：

#include < cstdio >
#include < cstring >
#define  lowbit(x) ((x)&(-(x)))
using   namespace  std;
const   int  kMaxn( 1007 );

int  n,ans,bit[kMaxn];

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

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

int  main()
{
     // freopen("data.in","r",stdin);

     while (scanf( " %d " , & n) == 1 )
    {
        ans = 0 ;
        memset(bit, 0 , sizeof (bit));

         for ( int  i = 1 ;i <= n;i ++ )
        {
             int  t;
            scanf( " %d " , & t);
            Add(t, 1 );
            ans += i - Sum(t - 1 ) - 1 ;
        }

        printf( " %d\n " ,ans);
    }

     return   0 ;
}