火柴排队——重温逆序对

 1 #include<algorithm>
 2 #include<iostream>
 3 #include<cstdio>
 4 using namespace std;
 5 const int N=100086,M=99999997;
 6 struct node{
 7     int x,p;
 8     bool operator < (const node oth) const {return x<oth.x;}
 9 }l[N],r[N];
10 int n,res,val[N],t[N];
11 void merge(int l,int mid,int r){
12     int pl=l,pr=mid+1;
13     for(int i=l;i<=r;i++)
14         if((pl<=mid)&&(pr>r||val[pl]<=val[pr]))
15             t[i]=val[pl++];
16         else
17             t[i]=val[pr++],res=(res+mid-pl+1)%M;
18     for(int i=l;i<=r;i++)val[i]=t[i];
19 }
20 void com(int l,int r){
21     if(l<r){
22         int mid=(l+r)>>1;
23         com(l,mid);
24         com(mid+1,r);
25         merge(l,mid,r);
26     }
27 }
28 int main(){
29     cin>>n;
30     for(int i=1;i<=n;i++)scanf("%d",&l[i].x),l[i].p=i;
31     for(int i=1;i<=n;i++)scanf("%d",&r[i].x),r[i].p=i;
32     sort(l+1,l+1+n);sort(r+1,r+1+n);
33     for(int i=1;i<=n;i++)val[l[i].p]=r[i].p;
34     com(1,n);
35     cout<<(res%M)<<endl;
36     return 0;
37 }