【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 ; }