Submission #1249016

#	Time	Username	Problem	Language	Result	Execution time	Memory
1249016		mirbek01	Mobile (BOI12_mobile)	C++20	0 / 100	559 ms	27964 KiB

mobile

#include <bits/stdc++.h>

using namespace std;

double dist(double x, double y, double a, double b) {
    return sqrt((x - a) * (x - a) + (y - b) * (y - b));
}

signed main() {
    int n, L;
    cin >> n >> L;

    vector <double> x(n), y(n);
    for (int i = 0; i < n; i++) {
        cin >> x[i] >> y[i];
        y[i] = abs(y[i]);
    }

    auto get_point = [&](int i, int j) {
        return max(0.0, min(L + 0.0, ((x[i] * x[i] + y[i] * y[i]) - (x[j] * x[j] + y[j] * y[j])) / (2.0 * (x[i] - x[j]))));
    };

    vector <double> start(n);
    vector <int> stk;
    for (int i = 0; i < n; i++) {
        if (!stk.empty() && x[stk.back()] == x[i]) {
            if (y[stk.back()] <= y[i]) {
                continue;
            } else {
                stk.pop_back();
            }
        }
        while (stk.size() > 1 && get_point(stk.back(), i) <= start[stk[stk.size() - 2]]) stk.pop_back();
        if (!stk.empty()) start[i] = get_point(stk.back(), i);
        stk.push_back(i);
    }

    double ans = 0;
    for (int i = 0; i + 1 < stk.size(); i++) {
        ans = max(ans, dist(x[stk[i]], y[stk[i]], start[stk[i]], 0));
        ans = max(ans, dist(x[stk[i]], y[stk[i]], start[stk[i + 1]], 0));
    }

    ans = max(ans, dist(x[stk.back()], y[stk.back()], start[stk.back()], 0));
    ans = max(ans, dist(x[stk.back()], y[stk.back()], L, 0));

    cout << fixed << setprecision(6) << ans << endl;
}

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