Submission #702621

#	Time	Username	Problem	Language	Result	Execution time	Memory
702621		nguyennehehe	Mobile (BOI12_mobile)	C++14	0 / 100	404 ms	8560 KiB

mobile

#include "bits/stdc++.h"
using namespace std;

const int INF = 1e9 + 7;

int32_t main() {
    cin.tie(0)->sync_with_stdio(0);
    
    int n, L; cin >> n >> L;
    vector<pair<int, int>> a(n);
    for (auto &x: a) cin >> x.first >> x.second;

    auto good = [&](double R) {
        vector<pair<double, double>> b;
        for (auto i: a) {
            long long u, v; tie(u, v) = i;
            #define sqr(x) (x) * (x)
            if (sqr(R) - sqr(v)) continue;
            double delta = sqrt(sqr(R) - sqr(v));
            double x1 = -delta + u, x2 = delta + u;
            b.emplace_back(x1, x2);
            // cout << fixed << setprecision(10) << x1 << ' ' << x2 << '\n';
        }
        
        sort(b.begin(), b.end());
        double l = 0;
        for (auto i: b) {
            if (i.first <= l) l = max(l, i.second);
        }
        return l >= L;
    };

    double l = -1, r = 1e9 + 1;
    for (int i = 1, ITER = 100; i <= ITER; ++i) {
        double m = l + (r - l) / 2;
        if (good(m)) r = m;
        else l = m;
    }
    cout << fixed << setprecision(10) << r;
}

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