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  1. #include<bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. #define ll long long
  6. #define ld long double
  7. #define vll vector<ll>
  8. #define pb push_back
  9. #define f first
  10. #define se second
  11. #define endl '\n'
  12. #define Left Node << 1
  13. #define Right Node << 1 | 1
  14. #define INF -1e9
  15. #define Fast() {ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);}
  16.  
  17. struct Point {
  18.     ld x, y;
  19. };
  20.  
  21.  
  22. void solve()
  23. {
  24.     int n;
  25.     cin >> n;
  26.  
  27.     vector<Point> a(n);
  28.     for (auto &[x, y] : a)
  29.         cin >> x >> y;
  30.  
  31.     int side = (a[0].y > 0 ? 1 : -1);
  32.     for (const auto &p : a) {
  33.         if ((p.y > 0 ? 1 : -1) != side) {
  34.             cout << -1 << endl;
  35.             return;
  36.         }
  37.     }
  38.  
  39.     auto check = [&](ld r) {
  40.         ld left = -1e30;
  41.         ld right = 1e30;
  42.  
  43.         for (auto [x, y] : a) {
  44.             y = fabsl(y);
  45.             ld v = 2 * r * y - y * y;
  46.  
  47.             if (v < 0)
  48.                 return false;
  49.  
  50.             ld d = sqrtl(v);
  51.  
  52.             left = max(left, x - d);
  53.             right = min(right, x + d);
  54.  
  55.             if (left > right)
  56.                 return false;
  57.         }
  58.  
  59.         return true;
  60.     };
  61.  
  62.     ld l = 0, r = 1e18;
  63.     for (int it = 0; it < 100; it++) {
  64.         ld mid = (l + r) / 2;
  65.  
  66.         if (check(mid))
  67.             r = mid;
  68.         else
  69.             l = mid;
  70.     }
  71.  
  72.     cout << fixed << setprecision(10) << (double)r << endl;
  73. }
  74.  
  75. int main()
  76. {
  77.     Fast();
  78.  
  79.     int t = 1;
  80.     // cin >> t;
  81.     while (t--)
  82.     {
  83.         solve();
  84.     }
  85.  
  86.     return 0;
  87. }
Success #stdin #stdout 0.04s 5320KB
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stdin
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Standard input is empty
stdout
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0.0000000000
https://ideone.com/DX1Wx0
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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