2015 HUAS Summer Trainning #4 A

 1 #include<iostream>
 2 #include<algorithm>
 3 using namespace std;
 4 const long long  maxn=500000+10;
 5 int a[maxn];
 6 long long  paisu(int x,int y)
 7 {
 8     if(x>=y) return 0;
 9     long long  cnt=0;
10     int m=x+(y-x)/2;
11     cnt+=paisu(x,m);
12     cnt+=paisu(m+1,y);
13     int p2=m+1;
14     for(int p1=x;p1<=m;p1++)
15     {
16         for(int j=p2;j<=y;j++)
17         {
18             if(a[p1]<a[j])
19                 break;
20             else p2++;
21         }
22         cnt+=p2-m-1;
23     }
24     sort(a+x,a+y+1);
25     return cnt;
26 
27 }
28 int main()
29 {
30     int i;
31     int n;
32     while(cin>>n&&n)
33     {
34         for(i=0;i<n;i++)
35             cin>>a[i];
36         cout<<paisu(0,n-1)<<endl;
37     }
38     return 0;
39 }