Submission #409968

#	Time	Username	Problem	Language	Result	Execution time	Memory
409968		BERNARB01	Mobile (BOI12_mobile)	C++17	0 / 100	749 ms	12060 KiB

mobile

#include <bits/stdc++.h>

using namespace std;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n, L;
	cin >> n >> L;
	vector<pair<int, int>> p(n);
	for (int i = 0; i < n; i++) {
		cin >> p[i].first >> p[i].second;
	}
	long double l = -1, r = 7;
	for (int itr = 0; itr < 14; itr++) {
		long double mid = (l + r) / 2.0;
		vector<pair<long double, long double>> v;
		int ok = 1;
		for (int i = 0; i < n; i++) {
			long double b = -2.0 * p[i].first;
			long double c = (p[i].first * p[i].first) + (p[i].second * p[i].second) - (mid * mid);
			long double delta = (b * b) - 4.0 * c;
			if (delta < 0) {
				continue;
			}
			long double lb = (-b - sqrtl(delta)) / 2.0, rb = (-b + sqrtl(delta)) / 2.0;
			if (lb > (long double) L) {
				continue;
			}
			while (!v.empty() && lb < v.back().first) {
				v.pop_back();
			}
			if (!v.empty() && v.back().second < lb) {
				ok = 0;
				break;
			}
			v.push_back({lb, rb});
		}
		if (v.empty() || !ok || (!v.empty() && ((min((long double) L, end(v)[-1].second) - max(v[0].first, (long double) 0.0)) < (long double) L))) {
			l = mid;
		} else {
			r = mid;
		}
	}
	cout << setprecision(4) << fixed << (r + l) / 2.0 << '\n';
	return 0;
}

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