小南梁刚学 OI 1145s，MLE 18pts 求调

#include<bits/stdc++.h>
// #pragma G++ optimize(2)
using namespace std;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using pii=pair<int,int>;
#define fi first
#define se second
constexpr int N=1e5+5;
int n;
struct line {
	int xl,xr,y,val;
} a[N*2];
bool cmp(line A,line B) {
	return A.y<B.y;
}
int b[N*2],tot;
int f(int x) {
	return lower_bound(b+1,b+n*2+1,x)-b;
}
ll v[N*16],w[N*16];
int ls(int p) {return p*2;}
int rs(int p) {return p*2+1;}
void pushup(int p,int pl,int pr) {
	if(v[p]) w[p]=b[pr]-b[pl];
	else if(pl+1==pr) w[p]=0;
	else w[p]=w[ls(p)]+w[rs(p)];
}
void add(int p,int pl,int pr,int l,int r,int x) {
	if(pl==l&&pr==r) {
		v[p]+=x;
		pushup(p,pl,pr);
		return;
	}
	int mid=(pl+pr)/2;
	if(l<mid) add(ls(p),pl,mid,l,min(r,mid),x);
	if(r>mid) add(rs(p),mid,pr,max(l,mid),r,x);
	pushup(p,pl,pr);
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	// freopen("P5490_3.in","r",stdin);
	// freopen("data.out","w",stdout);
	cin>>n;
	for(int i=1,xa,ya,xb,yb;i<=n;i++) {
		cin>>xa>>ya>>xb>>yb;
		a[i]={xa,xb,ya,1};
		a[i+n]={xa,xb,yb,-1};
		b[i]=xa;
		b[i+n]=xb;
	}
	sort(b+1,b+n*2+1);
	tot=unique(b+1,b+n*2+1)-(b+1);
	// for(int i=1;i<=tot;i++) cerr<<b[i]<<" ";
	// cerr<<"\n";
	sort(a+1,a+n*2+1,cmp);
	// for(int i=1;i<=n*2;i++) cerr<<a[i].xl<<" "<<a[i].xr<<" "<<a[i].y<<" "<<a[i].val<<"\n";
	// assert(a[1].val>0);
	add(1,1,tot,f(a[1].xl),f(a[1].xr),a[1].val);
	ll ans=0;
	for(int i=2;i<=n*2;i++) {
		int xl=f(a[i].xl),xr=f(a[i].xr);
		// cerr<<w[1]<<"\n";
		ans+=(a[i].y-a[i-1].y)*w[1];
		add(1,1,tot,xl,xr,a[i].val);
	}
	cout<<ans<<"\n";
	return 0;
}