喷水装置

题目描述

思路

代码

#include <cstdio>
#include <cmath>

int n, L, W, t, att, ans;
double w;
struct Node {
	double a, b;
} arr[15006], tmp;
inline void read(int &x) {
	int s = 0, f = 1;
	char ch = getchar();
	while (ch < '0' || ch > '9') {
		if (ch == '-') f = -1;
		ch = getchar();
	}
	while (ch >= '0' && ch <= '9') s = s * 10 + ch - '0', ch = getchar();
	x = s * f;
}
inline void write(int x) {
	if (x > 9) write(x / 10);
	putchar(x % 10 + '0');
}
void qsort(int L, int R) {
	int l = L, r = R;
	double mid = arr[l + r >> 1].a;
	while (l < r) {
		while (arr[l].a < mid) l++;
		while (arr[r].a > mid) r--;
		if (l <= r) {
			tmp = arr[l];
			arr[l] = arr[r];
			arr[r] = tmp;
			l++, r--;
		}
	}
	if (l < R) qsort(l, R);
	if (L < r) qsort(L, r);
}
int main() {
	read(t);
	while (t--) {
		ans = 0, att = 0;
		read(n), read(L), read(W);
		double w = W / 2.0, ww = w * w, wx;
		
		for (int i = 1, a, b; i <= n; ++i) {
			read(a), read(b);
			if (b <= w) continue;
			wx = sqrt(b * b - ww);
			arr[++att].a = a - wx;
			arr[att].b = a + wx;
		}
		qsort(1, att);
		double ta = 0.0, tb = 0.0, prea = 0, preb;
		while (ta < L) {
			tb = ta;
			for (int i = prea + 1; i <= att; ++i) {
				if (arr[i].a <= ta && arr[i].b > tb) {
					tb = arr[i].b;
					preb = i;
				} 
			}
			ans++;
			if (prea == preb) break;
			ta = tb, prea = preb;
		}
		if (ta >= L) write(ans), puts("");
		else puts("-1");
	}
	return 0;
}