逆序数（归并排序　） 

 题目链接：
 http://acm.nyist.net/JudgeOnline/problem.php?pid=117 
 1 #include <iostream>
 2 #include <cstdio>
 3 using namespace std;
 4 
 5 int a[1000001], b[1000001];
 6 long long count;　
 7 
 8 void Merge(int i, int m, int j){
 9     int k, x, y;
10     y = m;
11     for(k = i; k <= j; ++k) b[k] = a[k];
12     for(k = i, x = m + 1; i <= m && x <= j; k++){
13         if(b[i] <= b[x]) a[k] = b[i++];
14         else{
15             a[k] = b[x++];
16             count = count + m - i + 1;
17         }
18     }
19     while(i <= m) a[k++] = b[i++];
20     while(x <= j) a[k++] = b[x++];
21 }
22 
23 void Msort(int i, int j){
24     if(i < j){
25         int m = (i + j) / 2;
26         Msort(i, m);
27         Msort(m + 1, j);
28         Merge(i, m, j);
29     }
30 }
31 
32 int main()
33 {
34     int T, i, j, k, N;
35     scanf("%d",&T);
36     while(T--){
37         scanf("%d", &N);
38         for(i = 1; i <= N; ++i) scanf("%d",&a[i]);
39         count = 0;
40         Msort(1, N);
41         printf("%lld\n", count);
42     }
43     return 0;
44 }

 

posted @ 2013-07-09 20:24  YaLing  阅读(203)  评论(0)    收藏  举报