Submission #464162

#	Time	Username	Problem	Language	Result	Execution time	Memory
464162		dqk	Mobile (BOI12_mobile)	C++17	4 / 100	1099 ms	78336 KiB

mobile

#include <bits/stdc++.h>

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int n;
    double L;
    std::cin >> n >> L;
    std::vector<std::vector<int>> p(n, std::vector<int>(2, 0));
    for (int i = 0; i < n; ++i) {
        std::cin >> p[i][0] >> p[i][1];
        p[i][1] = abs(p[i][1]);
    }
    sort(p.begin(), p.end(), [](auto a, auto b) {
            if (a[1] == b[1]) return a[0] < b[0];
            return a[1] < b[1];
            });
    double d1 = sqrt(p[0][0] * p[0][0] + p[0][1] * p[0][1]);
    double d2 = sqrt((p[0][0] - L) * (p[0][0] - L) + p[0][1] * p[0][1]);
    double lo = 0, hi = std::max(d1, d2);
    while(hi - lo > 1e-3) {
        double mi = (lo + hi) / 2;
        std::vector<std::vector<double>> u;
        bool ltok = false;
        bool rtok = false;
        for (int i = 0; i < n; ++i) {
            double h = p[i][1];
            if (h > mi)
                continue;
            double lf = p[i][0] - sqrt(1ll * mi * mi - 1ll * h * h);
            double rt = p[i][0] + sqrt(1ll * mi * mi - 1ll * h * h);
            if (rt < 0.0 || lf > L)
                continue;
            lf = std::max(lf, 0.0);
            rt = std::min(rt, L);
            u.push_back({lf, rt});
            if (rt == L)
                rtok = true;
            if (lf == 0.0)
                ltok = true;
        }
        sort(u.begin(), u.end());
        bool ok = rtok & ltok;
        double rt = -1;
        for (int i = 0; i < (int)u.size() && ok; ++i) {
            if (i == 0) {
                rt = u[i][1];
            }
            else {
                if (u[i][0] > rt)
                    ok = false;
                rt = u[i][1];
            }
        }
        if (ok) {
            hi = mi;
        }
        else {
            lo = mi;
        }
    }
    std::cout << lo << "\n";
    return 0;
}

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