72pts -> 100pts 但不理解

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll mov=1e4+1;
ll n,ans,last,minn=1e9,maxx=-1e9;
struct node
{
	ll l,r,h,mark;
}line[10005];
struct tee
{
	ll len,sum,num;
	//len:covered length
	//sum:the count of whole cover
	//num:the number of the line covering without intersection 
	//l,r:the range of this point 
	bool lflag,rflag;
	//if the left point&the right point is covered (for combining) 
}tree[200005];
bool cmp(node x,node y)
{
	if(x.h!=y.h) return x.h<y.h;
	return x.mark>y.mark;
}
void pushup(ll w,ll l,ll r)
{
	if(tree[w].sum) 
	{
		tree[w].num=1;
		tree[w].len=r-l+1;
		tree[w].lflag=tree[w].rflag=1;
	}
	else if(l==r)
	{
		tree[w].num=0;
		tree[w].len=0;
		tree[w].lflag=tree[w].rflag=0;
	}
	else
	{
		tree[w].num=tree[2*w].num+tree[2*w+1].num;
		if(tree[2*w].rflag&&tree[2*w+1].lflag) tree[w].num--;
		tree[w].len=tree[2*w].len+tree[2*w+1].len;
		tree[w].lflag=tree[2*w].lflag;
		tree[w].rflag=tree[2*w+1].rflag;
	}
}
void add(ll w,ll l,ll r,ll ql,ll qr,ll mark)
{
	if(l>=ql&&qr>=r)
	{
		tree[w].sum+=mark;
		pushup(w,l,r);
		return ;
	}
	ll mid=(l+r)>>1;
	if(ql<=mid) add(2*w,l,mid,ql,qr,mark);
	if(qr>mid) add(2*w+1,mid+1,r,ql,qr,mark);
	pushup(w,l,r);
}
int main()
{
	cin>>n;
	for(ll i=1;i<=n;i++)
	{
		ll xx1,xx2,yy1,yy2;
		cin>>xx1>>yy1>>xx2>>yy2;
		maxx=max(maxx,max(xx1,xx2));
		minn=min(minn,min(xx1,xx2));
		line[(i<<1)-1]={xx1,xx2,yy1,1};
		line[(i<<1)]={xx1,xx2,yy2,-1};
	}
	n<<=1;
	if(minn<=0)
	{
		for(ll i=1;i<=n;i++)
		{
			line[i].l+=-minn+1;
			line[i].r+=-minn+1;
		}
		maxx-=minn;
	}
	sort(line+1,line+n+1,cmp);
	for(ll i=1;i<=n;i++)
	{
		//cout<<i<<" "<<line[i].l<<" "<<line[i].r<<" "<<line[i].mark<<endl;
		add(1,1,maxx,line[i].l,line[i].r-1,line[i].mark);//为什么line[i].r要减一？ 
		while(line[i].h==line[i+1].h&&line[i].mark==line[i+1].mark)
		{
			i++;
			add(1,1,maxx,line[i].l,line[i].r-1,line[i].mark);//为什么line[i].r要减一？
		}
		ans+=abs(tree[1].len-last);
		last=tree[1].len;
		ans+=tree[1].num*2*(line[i+1].h-line[i].h);
	}
	cout<<ans;
}