Frosh Week

 1 #include <stdio.h>
 2 #define MAX 1000000
 3 
 4 int arr[MAX+5],ass[MAX+5];
 5 __int64 cnt;
 6 
 7 void MergeSort(int low,int high){
 8     int mid,p,q,i;
 9     if(high-low==1)
10         return;
11     mid=low+((high-low)>>1);
12     MergeSort(low,mid);
13     MergeSort(mid,high);
14     p=low,q=mid,i=low;
15     while(p<mid||q<high){
16         if(q>=high||(p<mid&&arr[p]<=arr[q]))
17             ass[i++]=arr[p++];
18         else{
19             ass[i++]=arr[q++];
20             cnt+=mid-p;
21         }
22     }
23     for(i=low;i<high;i++)
24         arr[i]=ass[i];
25 }
26 
27 void scani(int &num){
28     char ch;
29     int flag;
30     while(ch=getchar(),(ch>‘9‘||ch<‘0‘)&&(ch!=‘-‘));
31     if(ch==‘-‘)
32         flag=-1,num=0;
33     else
34         flag=1,num=ch-‘0‘;
35     while(ch=getchar(),ch<=‘9‘&&ch>=‘0‘)
36         num=num*10+ch-‘0‘;
37     num*=flag;
38 }
39 
40 int main(){
41     int n,i;
42     while(~scanf("%d",&n)){
43         for(i=1;i<=n;i++)
44             scani(arr[i]);
45         cnt=0;
46         MergeSort(1,n+1);
47         printf("%I64d\n",cnt);
48     }
49     return 0;
50 }