【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: 47229052011-10-08 21:19:56Accepted268915MS240K1078 BC++pyyTest 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 INF0x7f7f7f7f#define MAXSIZE 1010int 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 ;}