Submission #973324

#	Time	Username	Problem	Language	Result	Execution time	Memory
973324		IdanRosen	Mobile (BOI12_mobile)	C++98	0 / 100	1078 ms	47336 KiB

mobile

#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef long double ld;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    ll n, l;
    cin >> n >> l;

    vector<pll> arr(n);
    for (auto &ref: arr) cin >> ref.first >> ref.second;

    ld start = 0;
    ld end = 1.42e9;
    while (end - start > 1e-4) {
        ld mid = start + (end - start) / 2;

        bool check = false;
        {
            vector<pair<ld, ld>> ranges(n);
            for (int i = 0; i < n; i++) {
                if (mid < arr[i].second) continue;

                ld center = arr[i].first;
                ld delta = sqrt(mid * mid - (ld) (arr[i].second * arr[i].second));
                ranges[i] = {center - delta, center + delta};
            }

            if (ranges.empty()) {
                check = false;
            } else {

                std::sort(ranges.begin(), ranges.end());

                vector<pair<ld, ld>> intersects;
                for (int i = 0; i < n; i++) {
                    if (intersects.empty())
                        intersects.push_back(ranges[i]);
                    else {
                        if (ranges[i].first <= intersects.back().second) {
                            intersects.back().second = max(intersects.back().second, ranges[i].second);
                        } else
                            intersects.push_back(ranges[i]);

                    }
                }

                for (auto& seg : intersects) {
                    if (seg.first <= 0 && l <= seg.second) {
                        check = true;
                        break;
                    }
                }
            }
        }

        if (check)
            end = mid;
        else
            start = mid;
    }

    cout << fixed << setprecision(6) << start << endl;
}

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