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  1. #include <iostream>
  2. #include <vector>
  3. #include <omp.h>
  4.  
  5. using namespace std;
  6.  
  7. void merge(vector<int>& arr, int l, int m, int r) {
  8.     int i, j, k;
  9.     int n1 = m - l + 1;
  10.     int n2 = r - m;
  11.     vector<int> L(n1), R(n2);
  12.  
  13.     for (i = 0; i < n1; i++) {
  14.         L[i] = arr[l + i];
  15.     }
  16.     for (j = 0; j < n2; j++) {
  17.         R[j] = arr[m + 1 + j];
  18.     }
  19.  
  20.     i = 0;
  21.     j = 0;
  22.     k = l;
  23.     while (i < n1 && j < n2) {
  24.         if (L[i] <= R[j]) {
  25.             arr[k++] = L[i++];
  26.         } else {
  27.             arr[k++] = R[j++];
  28.         }
  29.     }
  30. }
  31.  
  32. void merge_sort(vector<int>& arr, int l, int r) {
  33.     if (l < r) {
  34.         int m = l + (r - l) / 2;
  35.         #pragma omp task
  36.         merge_sort(arr, l, m);
  37.         #pragma omp task
  38.         merge_sort(arr, m + 1, r);
  39.         merge(arr, l, m, r);
  40.     }
  41. }
  42.  
  43. void parallel_merge_sort(vector<int>& arr) {
  44.     #pragma omp parallel
  45.     {
  46.         #pragma omp single
  47.         merge_sort(arr, 0, arr.size() - 1);
  48.     }
  49. }
  50.  
  51. int main() {
  52.     vector<int> arr = {5, 2, 9, 1, 7, 6, 8, 3, 4};
  53.     double start, end;
  54.  
  55.     // Measure performance of sequential merge sort
  56.     start = omp_get_wtime();
  57.     merge_sort(arr, 0, arr.size() - 1);
  58.     end = omp_get_wtime();
  59.     cout << "Sequential merge sort time: " << end - start << " seconds" << endl;
  60.  
  61.     // Measure performance of parallel merge sort
  62.     arr = {5, 2, 9, 1, 7, 6, 8, 3, 4};
  63.     start = omp_get_wtime();
  64.     parallel_merge_sort(arr);
  65.     end = omp_get_wtime();
  66.     cout << "Parallel merge sort time: " << end - start << " seconds" << endl;
  67.  
  68.     return 0;
  69. }
  70.  
Success #stdin #stdout #stderr 0.32s 40456KB
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Standard input is empty
stdout
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Standard output is empty
stderr
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Error: unexpected symbol in "using namespace"
Execution halted
https://ideone.com/mLC1zF
language:
R (R 3.5.2)
created:
16 days ago
visibility:
public

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