【树状数组+简单题】杭电 hdu 2689 Sort it

 

/* THE PROGRAM IS MADE BY PYY */

/*----------------------------------------------------------------------------//

    Copyright (c) 2011 panyanyany All rights reserved.

 

    URL   : http://acm.hdu.edu.cn/showproblem.php?pid=2689

    Name  : 2689 Sort it

 

    Date  : Saturday, October 8, 2011

    Time Stage : half an hour

 

    Result:

4722905

2011-10-08 21:19:56

Accepted

2689

15MS

240K

1078 B

C++

pyy

 

Test Data :

 

Review :

果然是比较水的题，当然，一开始有点犯蒙，看了下解题报告，

原来是跟逆序数对有关的，自己竟联系不起来，还想着把它们

逐一对换排序呢……

//----------------------------------------------------------------------------*/

 

#include <stdio.h>

#include <string.h>

 

#define INF        0x7f7f7f7f

 

#define MAXSIZE 1010

 

int n ;

int tree[MAXSIZE] ;

 

int lowbit (int x)

{

       return x & (-x) ;

}

 

void add (int pos, int val)

{

       while (pos <= n)

       {

              tree[pos] += val ;

              pos += lowbit (pos) ;

       }

}

 

int getSum (int pos)

{

       int sum = 0 ;

       while (pos > 0)

       {

              sum += tree[pos] ;

              pos -= lowbit (pos) ;

       }

       return sum ;

}

 

int main ()

{

       int i, j ;

       int x, sum ;

       while (scanf ("%d", &n) != EOF)

       {

              memset (tree, 0, sizeof (tree)) ;

              sum = 0 ;

              for (i = 1 ; i <= n ; ++i)

              {

                     scanf ("%d", &x) ;

                     sum += getSum (n) - getSum (x) ;

                     add (x, 1) ;

              }

              printf ("%d\n", sum) ;

       }

       return 0 ;

}