Submission #936015

#	Time	Username	Problem	Language	Result	Execution time	Memory
936015		cryan	Mobile (BOI12_mobile)	C++17	100 / 100	850 ms	25352 KiB

mobile

#include <bits/stdc++.h>
using namespace std;

#define sz(x) (int)x.size()

struct Point {
	double x, y;
};

/**
 * @returns the intersection of the perpendicular line that
 * crosses the midpoint of Points a & b with the highway
 */
double max_point(Point a, Point b) {
	return (b.x * b.x + b.y * b.y - a.x * a.x - a.y * a.y) / (2 * b.x - 2 * a.x);
}
/**
 * @returns the euclidean distance between Points a & b
 */
double dist(Point a, Point b) {
	return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

int main() {
	int n, l;
	cin >> n >> l;

	deque<Point> stck;
	for (int i = 0; i < n; i++) {
		Point cur;
		cin >> cur.x >> cur.y;
		cur.y = abs(cur.y);

		// take the one with the lowest y coord
		if (sz(stck) && stck.back().x == cur.x) {
			if (cur.y >= stck.back().y) {
				continue;
			} else if (cur.y < stck.back().y) {
				stck.pop_back();
			}
		}

		// find "crosses"
		while (sz(stck) > 1 && max_point(stck[sz(stck) - 2], stck.back()) > max_point(stck.back(), cur)) {
			stck.pop_back();
		}

		stck.push_back(cur);
	}

	// out of bounds
	while (sz(stck) > 1 && max_point(stck[0], stck[1]) < 0)
		stck.pop_front();
	while (sz(stck) > 1 && max_point(stck[sz(stck) - 2], stck.back()) > l)
		stck.pop_back();

	double ans = 0;
	for (int x = 0; x < sz(stck); x++) {
		Point left = {(x ? max_point(stck[x], stck[x - 1]) : 0), 0};
		Point right = {(x < sz(stck) - 1 ? max_point(stck[x], stck[x + 1]) : l), 0};

		if (left.x < 0 || right.x > l || right.x < 0 || left.x > l)
			continue;

		ans = max({ans, dist(stck[x], left), dist(stck[x], right)});
	}

	cout << fixed << setprecision(6) << ans << endl;
}

• Subtask 1: 4 / 4
• Subtask 2: 4 / 4
• Subtask 3: 4 / 4
• Subtask 4: 4 / 4
• Subtask 5: 4 / 4
• Subtask 6: 5 / 5
• Subtask 7: 5 / 5
• Subtask 8: 5 / 5
• Subtask 9: 5 / 5
• Subtask 10: 5 / 5
• Subtask 11: 5 / 5
• Subtask 12: 5 / 5
• Subtask 13: 5 / 5
• Subtask 14: 5 / 5
• Subtask 15: 5 / 5
• Subtask 16: 5 / 5
• Subtask 17: 5 / 5
• Subtask 18: 5 / 5
• Subtask 19: 5 / 5
• Subtask 20: 5 / 5
• Subtask 21: 5 / 5