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  1. //#include "stdafx.h"
  2. #include <vector>
  3. #include <chrono>
  4. #include <iostream>
  5.  
  6. using namespace std;
  7. using namespace std::chrono;
  8.  
  9. using number = double;
  10. const int n = 100000;
  11.  
  12. vector<number> x(n);
  13.  
  14. inline number Harry()
  15. {
  16.     number sum = 0;
  17.     number part = 0;
  18.  
  19.     for (int i = n - 1; i > 0; --i)
  20.     {
  21.         sum += x[i - 1] * (part += x[i]);
  22.     }
  23.     return sum;
  24. }
  25.  
  26. inline number VladD()
  27. {
  28.     number s = 0;
  29.     for (int i = 0; i < n; ++i) s += x[i];
  30.     number s2 = 0;
  31.     for (int i = 0; i < n; ++i) s2 += x[i] * x[i];
  32.     return (s * s - s2) / 2;
  33. }
  34.  
  35. int main(int argc, const char * argv[])
  36. {
  37.     for (int i = 0; i < x.size(); ++i)
  38.         x[i] = (number)rand();
  39.  
  40.     {
  41.         number sum = 0;
  42.         auto begin = steady_clock::now();
  43.         for (int i = 0; i < 10000; ++i) sum += VladD();
  44.         auto end = steady_clock::now();
  45.         cout << "sum = " << sum << ", elapsed time = " << duration_cast<milliseconds>(end - begin).count() << endl;
  46.     }
  47.  
  48.     {
  49.         number sum = 0;
  50.         auto begin = steady_clock::now();
  51.         for (int i = 0; i < 10000; ++i) sum += Harry();
  52.         auto end = steady_clock::now();
  53.         cout << "sum = " << sum << ", elapsed time = " << duration_cast<milliseconds>(end - begin).count() << endl;
  54.     }
  55. }
Success #stdin #stdout 3.73s 15240KB
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stdin
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Standard input is empty
stdout
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sum = 5.76149e+31, elapsed time = 2373
sum = 5.76149e+31, elapsed time = 1364
https://ideone.com/kTBpEL
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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