제출 #127089

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
127089		Mahmoud_Adel	Mobile (BOI12_mobile)	C++14	63 / 100	998 ms	82292 KiB

mobile

#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
typedef long long ll;
const int N = 1e6+5;
int n, m;
pair<long double, long double> p[N];
stack<pair<int, pair<long double, long double>>> s;
long double dis(int i, long double x)
{
	long double y = 0;
	return hypot((x-p[i].f), (y-p[i].s));
}
int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin >> n >> m;
	for(int i=0; i<n; i++) cin >> p[i].f >> p[i].s;
	for(int i=0; i<n; i++)
	{
		if(s.empty()) s.push({i, {0, m}});
		else
		{
			auto t = s.top();
			if(p[i].f == p[t.f].f || dis(t.f, t.s.s) < dis(i, t.s.s)) 
			continue;
			long double x;
			while(!s.empty() && dis(s.top().f, s.top().s.f) >= dis(i, s.top().s.f)) x = s.top().s.f, s.pop();
			if(s.empty())
			{ 
				s.push({i, {0, m}});
				continue;
			}
			t = s.top();
			if(dis(t.f, t.s.s) >= dis(i, t.s.s))
			{
				long double x1 = p[i].f, x2 = p[t.f].f;
				long double y1 = p[i].s, y2 = p[t.f].s;
				x = (x1*x1 - x2*x2 + y1*y1-y2*y2)/(2*x1-2*x2);
				if(x <= t.s.f) continue;
				s.pop();
				t.s.s = x;
				s.push(t);
			}
			s.push({i, {x, m}});
		}
	}
	long double ans = 0;
	while(!s.empty())
	{
		auto t = s.top();
		s.pop();
		ans = max(ans, max(dis(t.f, t.s.f), dis(t.f, t.s.s)));
	}
	cout << fixed << setprecision(7) << ans << endl;
}

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