Submission #884586

#	Time	Username	Problem	Language	Result	Execution time	Memory
884586		bedupako	Mobile (BOI12_mobile)	C++17	0 / 100	1102 ms	48420 KiB

mobile

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

#define all(x) x.begin(),x.end()
typedef long long ll;
const double E = 1e-9;

bool good(vector<pair<double,double>>& x, double l){
	int n = x.size();
	sort(all(x));
	stack<pair<double,double>> s;
	for(int i = 0; i < n; i++){
		if(s.empty()){
			s.push(x[i]);
		}else if(s.top().second >= x[i].first){
			s.top().second = max(s.top().second,x[i].second);
		}else{
			s.push(x[i]);
		}
	}
	if((int)s.size() == 1){
		if(abs(s.top().first) <= E and abs(s.top().second-l) <= E){
			return true;
		}
	}
	return false;
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n,l;
	cin >> n >> l;
	vector<double> x(n),y(n);
	for(int i = 0; i < n; i++){
		cin >> x[i] >> y[i];
	}
	double low = 0, high = 1e+10;
	double ans = 0l;
	int cnt = 0;
	while(high - low >= E and cnt <= 100){
		cnt++;
		//cout << "Iteration "  << cnt << '\n';
		double R = (low + high)/2;
		// cout << "Radius " << R << '\n';
		vector<pair<double,double>> ranges;
		for(int i = 0; i < n; i++){
			if(R < y[i]){
				continue;
			}else{
				double val = sqrt(R*R - y[i]*y[i]);
				ranges.emplace_back(max(0/1.0,(double)x[i]-val),
														min((double)l,(double)x[i]+val));
			}
		}
		if(good(ranges,l)){
			if(abs(R-ans) <= E){
				break;
			}
			ans = R;
			high = R - E;
		}else{
			low = R + E;
		}
	}
	cout << fixed << setprecision(6) <<  ans << '\n';
}

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