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  1. #include <iostream>
  2. #include <vector>
  3. #include <chrono>
  4. #include <algorithm>
  5.  
  6. template <typename timepoint_type>
  7. void display_time_difference(timepoint_type start, timepoint_type end)
  8. {
  9.     using namespace std::chrono;
  10.  
  11.     std::cout << "Took " << duration_cast<milliseconds>(end - start).count() ;
  12.     std::cout << " ms." << std::endl;
  13. }
  14.  
  15. int main()
  16. {
  17.     const unsigned outer_size = 10000;
  18.     const unsigned inner_size = 5000;
  19.  
  20.  
  21.     std::cout << "1) a 2D dynamic array of size " << outer_size ;
  22.     std::cout << " x " << inner_size << std::endl;
  23.  
  24.     auto start = std::chrono::high_resolution_clock::now();
  25.  
  26.     int** array2D = new int*[outer_size];
  27.     for (unsigned i = 0; i < outer_size; i++) 
  28.     {
  29.         array2D[i] = new int[inner_size];
  30.         std::fill(array2D[i], array2D[i] + inner_size, 1);
  31.     }
  32.  
  33.     auto end = std::chrono::high_resolution_clock::now();
  34.     display_time_difference(start, end);
  35.  
  36.     for (unsigned i = 0; i < outer_size; ++i)
  37.         delete [] array2D[outer_size-i-1];
  38.     delete [] array2D;
  39.  
  40.  
  41.     std::cout << "2) a 2D vector of size " << outer_size;
  42.     std::cout << " x " << inner_size << ", using resize" << std::endl;
  43.     start = std::chrono::high_resolution_clock::now();
  44.     {
  45.         std::vector<std::vector<int> > vec2D;
  46.         vec2D.resize(outer_size);
  47.         for (unsigned i = 0; i < outer_size; i++)
  48.         {
  49.             vec2D[i].resize(inner_size);
  50.             std::fill(vec2D[i].begin(), vec2D[i].end(), 1);
  51.         }
  52.  
  53.         end = std::chrono::high_resolution_clock::now();
  54.     }
  55.     display_time_difference(start, end);
  56.  
  57.  
  58.     std::cout << "3) a 2D vector of size " << outer_size;
  59.     std::cout << " x " << inner_size << ", using push_back" << std::endl;
  60.     start = std::chrono::high_resolution_clock::now();
  61.     {
  62.         std::vector<std::vector<int> > vec2D;
  63.         for (unsigned i = 0; i < outer_size; ++i)
  64.         {
  65.             vec2D.push_back(std::vector<int>());
  66.             std::vector<int>& v = vec2D.back();
  67.             for (unsigned j = 0; j < inner_size; ++j)
  68.                 v.push_back(1);
  69.         }
  70.         end = std::chrono::high_resolution_clock::now();
  71.     }
  72.     display_time_difference(start, end);
  73.  
  74.  
  75.     std::cout << "4) a 2D vector of size " << outer_size;
  76.     std::cout << " x " << inner_size << ", using constructors" << std::endl;
  77.     start = std::chrono::high_resolution_clock::now();
  78.     {
  79.         std::vector<std::vector<int>> vec2D(outer_size, std::vector<int>(inner_size, 1));
  80.         end = std::chrono::high_resolution_clock::now();
  81.     }
  82.     display_time_difference(start, end);
  83. }
Success #stdin #stdout 1.15s 3568KB
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Standard input is empty
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1) a 2D dynamic array of size 10000 x 5000
Took 185 ms.
2) a 2D vector of size 10000 x 5000, using resize
Took 250 ms.
3) a 2D vector of size 10000 x 5000, using push_back
Took 465 ms.
4) a 2D vector of size 10000 x 5000, using constructors
Took 183 ms.
https://ideone.com/Njdcz0
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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