Submission #656300

#	Time	Username	Problem	Language	Result	Execution time	Memory
656300		chjiao	Mobile (BOI12_mobile)	C++14	100 / 100	460 ms	16084 KiB

mobile

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

#define fastio	ios_base::sync_with_stdio(false);cin.tie(0)
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()

#define FOR(i,a,b) for(ll i=a;i<=b;i++)
#define FORB(i,a,b) for(ll i=a;i>=b;i--)

#define getbit(mask,i) ((mask>>(i))&1)
#define getnum(i) (1<<(i))

#define endl "\n"
#define sz(x) (int)size(x)
#define mp make_pair
using ll = long long;
const ll MOD1 = 1e9+7;
const ll MOD2 = 998244353;
const ll MN = 1e5;


//first true float/double
long double FLOAT_ERR = 1e-5;
long double first_true_float(long double lo, long double hi, function<bool(long double)> f) {
	// if none of the values in the range work, return hi + 1
	lo--;
	hi++;
	while (hi-lo > FLOAT_ERR) {
		long double mid =  (lo + hi) / 2.0f;
		if (f(mid)) {
			hi = mid;
		} else {
			lo = mid;
		}
	}
	return lo;
}

int main() {
    fastio;
	//freopen("XXX.in","r",stdin);
	// freopen("XXX.out","w",stdout);
	
	ll N, L;
	cin >> N >> L;
	vector<pair<ll, ll>> stations(N);
	FOR(i,0,N-1) {
		ll y;
		cin >> stations[i].first >> y;
		stations[i].second = y*y;
	}
	long double ans = first_true_float(1, 1.5e9, [&](long double mid) { 
		long double mx=0;
		long double dd=mid*mid, xx;
		for(auto station:stations) {
			if(dd-station.second<0) continue;
			xx=sqrt(dd-station.second);
			if(station.first-xx<=mx) 
				mx = max(mx, station.first+xx);
		}
		return mx>=L;
	});
	cout <<  fixed << setprecision(6) << ans << endl;

}

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