Submission #990600

#	Time	Username	Problem	Language	Result	Execution time	Memory
990600		Ska	Mobile (BOI12_mobile)	C++14	0 / 100	468 ms	13148 KiB

mobile

#include <bits/stdc++.h>
using namespace std;
 
const int N = 1e5 + 5;
 
int n;
long double m;
long double x[N], y[N];
 
pair<long double, long double> calc(long double r, int i) {
    if (r < y[i]) {
        return {-1, -1};
    }
    return {x[i] - sqrtl(r * r - y[i] * y[i]), x[i] + sqrtl(r * r - y[i] * y[i])};
}
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> n >> m;
    long double l = 2e9, r = 2e9;
    for (int i = 1; i <= n; ++i) {
        cin >> x[i] >> y[i];
        l = min(l, abs(y[i]));
    }
    int iter = 50;
    while (iter--) {
        vector<pair<long double, long double>> segments;
        long double mid = (l + r) / 2;
        for (int i = 1; i <= n; ++i) {
            auto x = calc(mid, i);
            if (x.first != -1 && x.second != -1) {
                segments.emplace_back(x.first, x.second);
            }
        }
        sort(segments.begin(), segments.end());
        long double bound = 0;
        for (auto x : segments) {
            bound = max(bound, x.second);
            if (bound >= m) {
                break;
            }
        }
        if (bound >= m) {
            r = mid;
        } else {
            l = mid;
        }
    }
    cout << fixed << setprecision(6) << l << '\n';
}

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