Submission #356767

#	Time	Username	Problem	Language	Result	Execution time	Memory
356767		penguinhacker	Mobile (BOI12_mobile)	C++14	28 / 100	1097 ms	57612 KiB

mobile

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

#define ll long long
#define ar array

const int mxN = 1000000;
int n, l, x[mxN], y[mxN];

bool ok(double d) {
	// vector<pair<double, double>> d;
	vector<pair<double, int>> e;
	for (int i = 0; i < n; ++i) {
		if (abs(y[i]) < d) {
			double r = sqrt(d * d - (ll)y[i] * y[i]);
			double ls = x[i] - r;
			double rs = x[i] + r;
			if (rs > 0 && ls < l) {
				ls = max(ls, 0.0);
				rs = min(rs, l + 1e-9);
				// d.emplace_back(ls, rs);
				e.emplace_back(ls, -1);
				e.emplace_back(rs, 1);
			}
		}
	}
	// for (auto& x : e) cout << x.first << " " << x.second << "\n";
	sort(e.begin(), e.end());
	if (e[0].first != 0 || e.back().first < l) return 0;
	int cur = 0;
	for (int i = 0; i < (int)e.size(); ++i) {
		cur -= e[i].second;
		if (i != (int)e.size() - 1 && cur <= 0) return 0;
	}
	return 1;
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout << fixed << setprecision(6);
	cin >> n >> l;
	for (int i = 0; i < n; ++i) cin >> x[i] >> y[i];
	double lb = 0, rb = 2e9;
	while(lb + (1e-7) < rb) {
		double mid = (lb + rb) / 2;
		if (ok(mid)) rb = mid;
		else lb = mid;
	}
	cout << lb;
	return 0;
}

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