Submission #754183

#	Time	Username	Problem	Language	Result	Execution time	Memory
754183		lukehsiao	Mobile (BOI12_mobile)	C++14	100 / 100	362 ms	35232 KiB

mobile

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

const int mxN = 1e6;
ll n, L, x[mxN], y[mxN];

bool works(double r) {
	double cur = 0;
	for (int i=0; i<n; ++i) {
		double d = r*r - y[i]*y[i];
		if (d >= 0) {
			double del = sqrt(d);
			if (x[i]-del <= cur)
				cur = max(cur, x[i]+del);
		}
	}
	return cur >= L;
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	cin >> n >> L;
	for (int i=0; i<n; ++i)
		cin >> x[i] >> y[i];
	
	double lo = 0, hi = 3e9;
	while (hi-lo > 1e-3) {
		double mid = (lo+hi)/2;
		if (works(mid))
			hi = mid;
		else
			lo = mid;
	}

	cout << fixed << setprecision(4) << (lo+hi)/2 << '\n';
}

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