Submission #432326

#	Time	Username	Problem	Language	Result	Execution time	Memory
432326		four_specks	Mobile (BOI12_mobile)	C++17	50 / 100	1097 ms	48264 KiB

mobile

#include <bits/stdc++.h>

using namespace std;

void solve()
{
    struct point
    {
        long x, y;
    };

    int n;
    long l;
    cin >> n >> l;

    vector<point> coords(n);
    for (int i = 0; i < n; i++)
        cin >> coords[i].x >> coords[i].y;

    auto valid = [&](const double &d) -> bool
    {
        vector<pair<double, double>> cov;
        for (auto [x, y] : coords)
        {
            if (y * y < d * d)
            {
                double h = sqrt(d * d - y * y);
                cov.emplace_back(x - h, x + h);
            }
        }
        sort(cov.begin(), cov.end());

        bool ended = 0;
        double e = 0.0;
        for (auto [x1, x2] : cov)
        {
            if (x1 <= e)
            {
                e = max(e, x2);
                if (e >= l)
                {
                    ended = 1;
                    break;
                }
            }
            else
                break;
        }

        return ended;
    };

    double ans = 1e15;
    for (double lo = 0.5; ans - lo > 1e-5;)
    {
        if (double mid = (lo + ans) / 2.0; valid(mid))
            ans = mid;
        else
            lo = mid + 1e-4;
    }

    cout << fixed << setprecision(5) << ans << '\n';
}

int main()
{
    ios_base::sync_with_stdio(false), cin.tie(NULL);

    solve();

    return 0;
}

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