题解

#include <bits/stdc++.h>
using namespace std;
 
const int Max=100105;
const int mod=99999997;
struct px{int bh,num;};
px a[Max],b[Max];
long long c[Max],r[Max];
long long n,sum;
 
int get_int()
{
   int x=0,f=1;
   char c;
   for(c=getchar();(c<'0'||c>'9')&&(c!='-');c=getchar());
   if(c=='-') {f=-1; c=getchar();}
   for(;c>='0'&&c<='9';c=getchar()) x=(x<<3)+(x<<1)+c-'0';
   return x*f;
}
 
bool comp(const px &a,const px &b)
{
   return a.num<b.num;
}
 
void merge(int s,int mid,int t)
{
   int i=s,k=s,j=mid+1;
   while(i<=mid&&j<=t)
   {
   	 if(c[i]>c[j])
   	 {
   	   r[k++]=c[j++];
   	   sum+=mid-i+1;
   	 }
   	 else r[k++]=c[i++];
   }
 
   while(i<=mid) r[k++]=c[i++];
   while(j<=t) r[k++]=c[j++];
   for(int x=s;x<=t;x++) c[x]=r[x];
}
 
void mergesort(int s,int t)
{
   if(s<t)
   {
     int mid=(s+t)/2;
     mergesort(s,mid);
     mergesort(mid+1,t);
     merge(s,mid,t);
   }
}
 
int main()
{
   n=get_int();
   for(int i=1;i<=n;i++)
   {
   	 a[i].num=get_int();
   	 a[i].bh=i;
   }
   for(int i=1;i<=n;i++)
   {
   	 b[i].num=get_int();
   	 b[i].bh=i;
   }
   sort(a+1,a+n+1,comp);
   sort(b+1,b+n+1,comp);
 
   for(int i=1;i<=n;i++) c[b[i].bh]=a[i].bh;
 
   mergesort(1,n);
 
   cout<<sum%mod<<endl;
   return 0;
}