计算几何 扫描线 矩形面积并

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#define x first
#define y second
using namespace std;
typedef pair<int, int> PII;
const int N = 1010;

typedef long long LL;
int n;
PII l[N], r[N]; //左上角和右下角

PII q[N];//高度区间

LL range_area(int a, int b) {
    
    
	int cnt = 0;
	for (int i = 0; i < n; i++) {
    
    
		if (l[i].x <= a && r[i].x >= b) {
    
    
			q[cnt++] = {
    
    l[i].y, r[i].y};
		}
	}
	if (!cnt)
		return 0;
	sort(q, q + cnt);
	LL res = 0;
	int st = q[0].x, ed = q[0].y;
	for (int i = 1; i < cnt; i++) {
    
    
		if (q[i].x <= ed)
			ed = max(ed, q[i].y);
		else {
    
    
			res += ed - st;
			st = q[i].x, ed = q[i].y;
		}
	}
	res += ed - st;
	return res * (b - a);

}


int main() {
    
    
	cin >> n;
	vector<int>xs;
	for (int i = 0; i < n; i++) {
    
    
		cin >> l[i].x >> l[i].y >> r[i].x >> r[i].y;
		xs.push_back(l[i].x), xs.push_back(r[i].x); //离散化
	}
	sort(xs.begin(), xs.end());
	LL res = 0;
	for (int i = 0; i + 1 < xs.size(); i++) {
    
    
		if (xs[i] != xs[i + 1]) {
    
    
			res += range_area(xs[i], xs[i + 1]);
		}
	}
	cout << res << endl;
	return 0;

}