제출 #596245

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
596245		hail	Mobile (BOI12_mobile)	C++17	9 / 100	1093 ms	15956 KiB

mobile

#include <bits/stdc++.h>

using namespace std;

using pd = pair<double, double>;

int max_ind{};
int max_x{};

#define mp make_pair

int n;
double l;
int max_reach{};
pd station[(int)1e6];

pd intercept(pd coor, double r)
{
    if(abs(coor.second)>r) return mp(-1, -1);
    double mid = pow(r, 2)-pow(coor.second, 2);
    double rt_mid = pow(mid , 0.5);
    return mp(coor.first-rt_mid, coor.first+rt_mid);
}

bool check_dist(double r)
{
    if(r<0) return false;
    pd ret_int;
    double from_x = (intercept(station[max_reach], r)).second;
    /*
    auto it=lower_bound(station.begin(), station.end(), mp(-r, -1e9));
    while(it<station.end())
    {
        if((*it).first>from_x+r) return false;
        ret_int=intercept(*it, r);
        if(ret_int.first<=from_x && ret_int.second>from_x)
        {
            from_x=ret_int.second;
            if(from_x>=l) return true;
            it = upper_bound(it+1, station.end(), mp(from_x-r, 1e9));
        }
        else it++;
    }
    return false;
    */

   int last_reached{};
   pd circ;
    for(int i=max_reach+1; i<n; i++)
    {
        circ=station[i];
        if(circ.first>from_x+r)
        {
            max_reach=last_reached;
            return false;
        }
        if(circ.first>from_x-r)
        {
            ret_int=intercept(circ, r);
            if(ret_int.first<=from_x && ret_int.second>from_x)
            {
                from_x=ret_int.second;
                last_reached=i;
                if(from_x>=l) return true;
            }
        }
        
    }

    return false;
}


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

    cout<<setprecision(20); 

    cin>>n>>l;

    double max_coor{};

    for(int i=0; i<n; i++)
    {
        cin>>station[i].first>>station[i].second;
        max_coor=max({abs(station[i].first), abs(station[i].second), max_coor});
    }

    double high=2*(max_coor+l);
    double low=0;
    double mid;
    while(high-low>=1e-3)
    {
        mid=(high+low)/2;
        if(check_dist(mid)) high=mid;
        else low=mid;
    }

    cout<<high;

}

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