【HDU1255】覆盖的面积【线段树】【矩形面积交】

【题目链接】

再记录一个rep数组,表示当前区间至少被覆盖2次的长度。

/* Pigonometry */
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

typedef double DB;

const int maxn = 1005;

int n, m, tot, tr[maxn << 4];
DB sum[maxn << 4], rep[maxn << 4], disc[maxn << 1];

struct _line {
	DB x1, x2, y;
	int c;

	bool operator < (const _line &l) const {
		return y < l.y;
	}
} line[maxn << 1];

inline int find(DB x) {
	int l = 1, r = tot;
	while(l <= r) {
		int mid = l + r >> 1;
		if(disc[mid] < x) l = mid + 1;
		else if(disc[mid] == x) return mid;
		else r = mid - 1;
	}
}

inline void pushup(int p, int l, int r) {
	if(tr[p]) sum[p] = disc[r + 1] - disc[l];
	else if(l == r) sum[p] = 0;
	else sum[p] = sum[p << 1] + sum[p << 1 | 1];

	if(tr[p] >= 2) rep[p] = disc[r + 1] - disc[l];
	else if(l == r) rep[p] = 0;
	else if(tr[p] == 1) rep[p] = sum[p << 1] + sum[p << 1 | 1];
	else rep[p] = rep[p << 1] + rep[p << 1 | 1];
}

inline void insert(int p, int l, int r, int x, int y, int c) {
	if(x == l && r == y) {
		tr[p] += c;
		pushup(p, l, r);
		return;
	}
	int mid = l + r >> 1;
	if(y <= mid) insert(p << 1, l, mid, x, y, c);
	else if(x > mid) insert(p << 1 | 1, mid + 1, r, x, y, c);
	else {
		insert(p << 1, l, mid, x, mid, c);
		insert(p << 1 | 1, mid + 1, r, mid + 1, y, c);
	}
	pushup(p, l, r);
}

int main() {
	int T; scanf("%d", &T);
	while(T--) {
		scanf("%d", &n); m = n << 1;

		tot = 0;
		for(int i = 1; i <= n; i++) {
			DB x1, y1, x2, y2; scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);

			tot++;
			line[tot] = (_line){x1, x2, y1, 1};
			disc[tot] = x1;

			tot++;
			line[tot] = (_line){x1, x2, y2, -1};
			disc[tot] = x2;
		}

		sort(disc + 1, disc + 1 + tot);

		memset(tr, 0, sizeof(tr)); memset(sum, 0, sizeof(sum)); memset(rep, 0, sizeof(rep));
		sort(line + 1, line + 1 + m);

		DB ans = 0;
		for(int i = 1; i < m; i++) {
			int l = find(line[i].x1), r = find(line[i].x2);
			insert(1, 1, tot, l, r - 1, line[i].c);
			ans += rep[1] * (line[i + 1].y - line[i].y);
		}

		printf("%.2f\n", ans);
	}
	return 0;
}


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