Submission #1011160

#	Time	Username	Problem	Language	Result	Execution time	Memory
1011160		vjudge1	Mobile (BOI12_mobile)	C++17	0 / 100	291 ms	16796 KiB

mobile

#include <bits/stdc++.h>
using i64 = long long;

struct Point {
    double x, y;
};

double dist(const Point &a, const Point &b) {
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    return std::sqrt(dx * dx + dy * dy);
}

double insec(const Point &a, const Point &b) {
    double t1 = b.x * b.x + b.y * b.y - a.x * a.x - a.y * a.y;
    double t2 = b.x - a.x;
    return t1 / t2 / 2;
}

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

    int n;
    double len;
    std::cin >> n >> len;

    double ans = 0;

    Point l{0, 0}, r{len, 0}, pre, cur;
    for (int i = 0; i < n; i++) {
        auto &[x2, y2] = cur;
        std::cin >> x2 >> y2;

        ans = std::max(ans, std::min(dist(l, cur), dist(r, cur)));
        if (i != 0) {
            auto [x1, y1] = pre;
            if (y1 == y2) {
                continue;
            }
            double x0 = insec(pre, cur);
            if (x0 > 0 && x0 < len) {
                Point mid{x0, 0};
                ans = std::max(ans, std::min(dist(pre, mid), dist(cur, mid)));
            }
        }
        
        pre = cur;
    }
    std::cout << std::fixed << std::setprecision(6) << ans << "\n";

    return 0;
}

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