Submission #1056923

#	Time	Username	Problem	Language	Result	Execution time	Memory
1056923		TimAni	Mobile (BOI12_mobile)	C++17	0 / 100	1082 ms	25536 KiB

mobile

// time-limit: 3000
 
#include <bits/stdc++.h>
 
using namespace std;
using ll = long long;
 
const double eps = 1E-4;
 
struct point {
    int x{}, y{};
};
 
void solve() {
    int n, L;
    cin >> n >> L;
    vector<point> p(n);
    for(int i = 0; i < n; i++) {
        cin >> p[i].x >> p[i].y;
    }
    auto intersection = [&](const point& A, double R) -> array<double, 2> {
        if(abs(A.y) > R) {
            return {1e18, -1e18};
        }
        double D = 1.0 * R * R - 1.0 * A.y * A.y; // divided by 4
        double x1 = A.x - sqrt(D);
        double x2 = A.x + sqrt(D);
        if(x2 < x1) swap(x1, x2);
        return {x1, x2};
    };
 
    auto good = [&](double R) {
        vector<array<double, 2>> segs;
        for(int i = 0; i < n; i++) {
            if(abs(p[i].y) > R) continue;
            segs.push_back(intersection(p[i], R));
        }
        if(segs.empty()) return false;
        sort(segs.begin(), segs.end());
        int i = 0;
        double r = 0;
        while(i + 1 < n && segs[i + 1][0] <= r) {
            r = max(r, segs[i + 1][1]);
        }
        return r >= L;
    };
 
    double l = 0, r = 4e9;
    while(r - l > eps) {
        double R = (r + l) / 2;
        if(good(R)) {
            r = R;
        }
        else {
            l = R;
        }
    }
    cout << fixed << setprecision(-log10(eps)) << r << endl;
}
 
int main() {
    cin.tie(0)->sync_with_stdio(0);
    double T = 1;
    //cin >> T;
    while(T--) solve();
    return 0;
}

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