Submission #551197

#	Time	Username	Problem	Language	Result	Execution time	Memory
551197		narcissus	Mobile (BOI12_mobile)	C++17	0 / 100	775 ms	24600 KiB

mobile

#include <iostream>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{
    int n, l;
    cin >> n >> l;
    pair<int, int> coords[n];
    for (int i = 0; i < n; i++) {
        cin >> coords[i].first >> coords[i].second;
    }

    double low = 0, high = l;
    while (high - low >= 1e-3) {
        double mid = low + (high - low) / 2;
        // cout << mid << ":" << endl;
        bool flag = true;
        pair<double, double> inter, prevInter;
        double minv = l, maxv = 0;
        for (int i = 0; i < n; i++) {
            int x = coords[i].first;
            int y = coords[i].second;
            double xdist = sqrt(pow(mid, 2) - pow(y, 2));
            double a1 = max((double)0, -xdist + x);
            double a2 = min((double)l, xdist + x);
            minv = min(minv, a1);
            maxv = max(maxv, a2);
            // cout << "a " << a1 << ' ' << a2 << endl;
            inter = {a1, a2};
            if (i) {
                if (a1 > prevInter.second) {
                    flag = false;
                    break;
                }
            }
            prevInter = inter;
        }
        if (flag && minv <= 0 && maxv >= l) {
            high = mid;
        } else {
            low = mid;
        }
    }
    cout << high << endl;

    return 0;
}

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