Submission #1109851

#	Time	Username	Problem	Language	Result	Execution time	Memory
1109851		vjudge1	Mobile (BOI12_mobile)	C++17	8 / 100	1063 ms	24496 KiB

mobile

#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

int main() {
  int N, L;
  cin >> N >> L;
  vector<pair<int, int>> tr(N);
  for (auto& p : tr) cin >> p.first >> p.second;

  double low = 0, high = 3 * 1e9;
  while (low + 1e-5 < high) {
    double r = (high + low) / 2;
    vector<pair<double, double>> s;
    for (auto& p : tr) {
      if (abs(p.second) >= r) continue;
      double x = sqrt(r* r - p.second * p.second);
      double x1 = p.first - x, x2 = p.first + x;

      // x2 >= s.back().first is always true. That's why we can use merge with stack.
      while (!s.empty() && s.back().second >= x1) {
        x1 = min(x1, s.back().first);
        x2 = max(x2, s.back().second);
        s.pop_back();
      }
      s.push_back({x1, x2});
    }

    bool ok = false;
    for (auto& p : s) {
      if (p.first <= 0 && p.second >= L) {
        ok = true;
      }
    }
    if (ok) {
      high = r;
    } else {
      low = r;
    }
  }
  cout << high << endl;
  return 0;
}

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