[树状数组] PKU 2299 Ultra-QuickSort

[树状数组] PKU 2299 Ultra-QuickSort

维护名次即可（不需要离散化）。

# include  < stdio.h >
# include  < string .h >
# include  < algorithm >
using   namespace  std;

# define N  500005

typedef  long   long   int  LL;
int  n;
LL a[N];
int  r[N], s[N], c[N];
/* ************************************************* */
int  getsum( int  x)
{
                 int  ret  =   0 ;
                 while  (x  >   0 ) ret  +=  c[x], x   -=  x & ( - x);
                 return  ret;
}
void  inc( int  x)
{
                 while  (x  <=  n)  ++  c[x], x  +=  x & ( - x);
}
/* ************************************************* */
bool  cmp( int  x,  int  y)
{
                 return  a[x]  >  a[y];
}
int  main()
{
                LL ans;
                 int  i;
                 while  (scanf( " %d " ,  & n), n)
                {
                                memset(c + 1 ,  0 ,  sizeof (c[ 0 ]) * n);
                                 for  (i  =   0 ; i  <  n;  ++ i)
                                                r[i]  =  i, scanf( " %lld " ,  & a[i]);
                                sort(r, r + n, cmp);
                                 for  (i  =   0 ; i  <  n;  ++ i) s[r[i]]  =  i;
                                ans  =   0 ;
                                 for  (i  =   0 ; i  <  n;  ++ i)
                                                ans  +=  getsum(s[i] + 1 ), inc(s[i] + 1 );
                                printf( " %lld\n " , ans);
                }

                 return   0 ;
}