Submission #1093840

#	Time	Username	Problem	Language	Result	Execution time	Memory
1093840		damamila	Mobile (BOI12_mobile)	C++17	0 / 100	337 ms	21484 KiB

mobile

#include <bits/stdc++.h>

using namespace std;

//~ #define int long long

int n;
double l;
vector<pair<int, int>> points;

pair<double, double> circle_intersection(int i, double r) {
	auto [x, y] = points[i];
	if (y > r) return {-1, -1}; //too far away
	double r2 = r*r;
	double y2 = y*y;
	double tmp = sqrt(r2-y2);
	double x1 = x-tmp;
	double x2 = x+tmp;
	return {x1, x2};
}

void solve() {
	double ub = 1.5e9, lb = 1;
	double m;
	while (lb+0.001 < ub) {
		m = (lb+ub)/2;
		double reach = 0;
		bool ja = 1;
		for (int i = 0; i < n; i++) {
			auto [x1, x2] = circle_intersection(i, m);
			if (reach < x1) ja = 0;
			reach = max(reach, x2);
		}
		if (reach < l) ja = 0;
		if (ja) ub = m;
		else lb = m;
	}
	cout << lb << endl;
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);  
	cin >> n >> l;
	cout << fixed << setprecision(4);
	points = vector<pair<int, int>> (n);
	for (int i = 0; i < n; i++) {
		cin >> points[i].first >> points[i].second;
		//~ points[i].second = abs(points[i].second);
	}
	//~ sort(points.begin(), points.end());
	solve();
}

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