Submission #1236811

#	Time	Username	Problem	Language	Result	Execution time	Memory
1236811		cjspd_oly	Mobile (BOI12_mobile)	C++17	0 / 100	110 ms	8264 KiB

mobile

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

const double EPS = 1e-6;

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

    int N;
    double L;
    cin >> N >> L;

    vector<pair<int, int>> stations(N);
    for (int i = 0; i < N; ++i)
        cin >> stations[i].first >> stations[i].second;

    auto dist = [](double x, int px, int py) -> double {
        double dx = x - px;
        double dy = -py;
        return sqrt(dx * dx + dy * dy);
    };

    auto getClosestDist = [&](double x) -> double {
        int lo = 0, hi = N - 1;
        while (hi - lo > 3) {
            int mid = (lo + hi) / 2;
            if (stations[mid].first < x)
                lo = mid;
            else
                hi = mid;
        }

        double minD = DBL_MAX;
        for (int i = max(0, lo - 2); i <= min(N - 1, hi + 2); ++i) {
            minD = min(minD, dist(x, stations[i].first, stations[i].second));
        }
        return minD;
    };

    double l = 0, r = L;
    while (r - l > EPS) {
        double m1 = l + (r - l) / 3;
        double m2 = r - (r - l) / 3;

        double d1 = getClosestDist(m1);
        double d2 = getClosestDist(m2);

        if (d1 < d2)
            l = m1;
        else
            r = m2;
    }

    double result = getClosestDist((l + r) / 2.0);
    cout << fixed << setprecision(10) << result << '\n';

    return 0;
}

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