Submission #1079723

#	Time	Username	Problem	Language	Result	Execution time	Memory
1079723		EmmaXII	Mobile (BOI12_mobile)	C++17	0 / 100	286 ms	31592 KiB

mobile

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

typedef long long ll;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;

#define all(x) x.begin(), x.end()


int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(NULL);

	int N;
	ll L;
	cin >> N >> L;

	vector<ll> X(N);
	vector<ll> Y(N);
	for (int i=0;i<N;i++) cin >> X[i] >> Y[i];

	auto get_hw = [&](double y, double r) {
		if (abs(y) > r) return -1.0;
		return sqrt((r-y) * (r+y));
	};

	auto can_do = [&](double R) {
		double progress = 0.;
		for (int i=0;i<N;i++) {
			double hw = get_hw((double)Y[i], R);
			if (hw < 0) continue;

			double l = (double)X[i] - hw;
			double r = (double)X[i] + hw;
			if (l < progress) progress = r;
			if (progress >= (double)L) return true;
		}
		
		return false;
	};

	double lo = 0;
	ll lhi = L + abs(X[0]) + abs(Y[0]);
	lhi = lhi*lhi;
	for (int i=0;i<N;i++) {
		ll nhi = max(
			X[i]*X[i] + Y[i]*Y[i],
			(X[i]-L)*(X[i]-L) + Y[i]*Y[i]
		);
		lhi = min(nhi, lhi);
	}
	double hi = sqrt(lhi);

	while (hi - lo > 5e-4) {
		double mid = (lo + hi) / 2;
		if (can_do(mid)) hi = mid;
		else lo = mid;
	}
	cout << setprecision(10);
	cout << lo << endl;

	return 0;
}

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