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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4. struct timeit {
  5.     decltype(chrono::high_resolution_clock::now()) begin;
  6.     const string label;
  7.     timeit(string label = "???") : label(label) { begin = chrono::high_resolution_clock::now(); }
  8.     ~timeit() {
  9.         auto end = chrono::high_resolution_clock::now();
  10.         auto duration = chrono::duration_cast<chrono::milliseconds>(end - begin).count();
  11.         cerr << duration << "ms elapsed [" << label << "]" << endl;
  12.     }
  13. };
  14. const int iters = 1e1;
  15.  
  16. const int DIM1 = 100000;
  17. const int DIM2 = 100;
  18. int A[DIM1][DIM2];
  19. signed main() {
  20.     for (int i = 0; i < DIM1; i++) {
  21.         for (int j = 0; j < DIM2; j++) {
  22.             A[i][j] = rand() % 100;
  23.         }
  24.     }
  25.     {
  26.         timeit x("correct order");
  27.         for (int iter = 0; iter < iters; iter++)
  28.             for (int i = 0; i < DIM1; i++)
  29.                 for (int j = 0; j < DIM2; j++)
  30.                     A[i][j]++;
  31.  
  32.     }
  33.     {
  34.         timeit x("incorrect order");
  35.         int overall = 0;
  36.         for (int iter = 0; iter < iters; iter++) {
  37.             for (int j = 0; j < DIM2; j ++)
  38.                 for (int i = 0; i < DIM1; i++)
  39.                     A[i][j]++;
  40.         }
  41.     }
  42. }
Success #stdin #stdout #stderr 0.9s 42648KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
stderr
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60ms elapsed [correct order]
740ms elapsed [incorrect order]
https://ideone.com/PUJhdP
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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