洛谷P1966 [NOIP2013 提高组] 火柴排队

#include<bits/stdc++.h>
using namespace std;

const int N=1e5+10,M=1e8-3;
int p[N],tmp[N],cnt=0;

struct FF{
	int h,fi; 
}fs1[N],fs2[N];

bool cmp(FF x,FF y){
	return x.h<y.h;
}

void merge_sort(int l,int r){
	if(l>=r) return ;
	int mid=l+r>>1;
	merge_sort(l,mid);
	merge_sort(mid+1,r);
	
	int k=0,i=l,j=mid+1;
	while(i<=mid&&j<=r){
		if(p[i]<=p[j]) tmp[k++]=p[i++];
		else{
			cnt+=mid-i+1;
			cnt%=M;
			tmp[k++]=p[j++];
		} 
	}
	while(i<=mid) tmp[k++]=p[i++];
	while(j<=r) tmp[k++]=p[j++];
	for(int i=l,j=0;i<=r;i++,j++){
		p[i]=tmp[j];
	}
}

int main(){
	int n,h;
	cin>>n;
	for(int i=0;i<n;i++){
		scanf("%d",&h);
		fs1[i].h=h;
		fs1[i].fi=i;
	}
	for(int i=0;i<n;i++){
		scanf("%d",&h);
		fs2[i].h=h;
		fs2[i].fi=i;
	}
	sort(fs1,fs1+n,cmp);
	sort(fs2,fs2+n,cmp);
	
	for(int i=0;i<n;i++){
		p[fs2[i].fi]=fs1[i].fi;
	}
	merge_sort(0,n-1);
	cout<<cnt;
	return 0;
}