TheAlgorithms-C-Plus-Plus/sorting/shell_sort2.cpp

#include <array>
#include <cstdlib>
#include <ctime>
#include <iostream>

// for std::swap
#include <utility>

template <class T> void show_data(T *arr, size_t LEN) {
  size_t i;

  for (i = 0; i < LEN; i++)
    std::cout << arr[i] << ", ";
  std::cout << std::endl;
}

template <class T, size_t N> void show_data(T (&arr)[N]) { show_data(arr, N); }

/**
 * Optimized algorithm - takes half the time by utilizing
 * Mar
 **/
template <class T> void shell_sort(T *arr, size_t LEN) {
  const unsigned int gaps[] = {701, 301, 132, 57, 23, 10, 4, 1};
  const unsigned int gap_len = 8;
  size_t i, j, g;

  for (g = 0; g < gap_len; g++) {
    unsigned int gap = gaps[g];
    for (i = gap; i < LEN; i++) {
      T tmp = arr[i];

      for (j = i; j >= gap && (arr[j - gap] - tmp) > 0; j -= gap)
        arr[j] = arr[j - gap];

      arr[j] = tmp;
    }
  }
}

template <class T, size_t N> void shell_sort(T (&arr)[N]) {
  shell_sort(arr, N);
}

/**
 * function to compare sorting using cstdlib's qsort
 **/
int compare(const void *a, const void *b) {
  int arg1 = *static_cast<const int *>(a);
  int arg2 = *static_cast<const int *>(b);

  if (arg1 < arg2)
    return -1;
  if (arg1 > arg2)
    return 1;
  return 0;

  //  return (arg1 > arg2) - (arg1 < arg2); // possible shortcut
  //  return arg1 - arg2; // erroneous shortcut (fails if INT_MIN is present)
}

int main(int argc, char *argv[]) {
  int i, NUM_DATA;

  if (argc == 2)
    NUM_DATA = atoi(argv[1]);
  else
    NUM_DATA = 200;

  // int array = new int[NUM_DATA];
  int *data = new int[NUM_DATA];
  int *data2 = new int[NUM_DATA];
  // int array2 = new int[NUM_DATA];
  int range = 1800;

  std::srand(time(NULL));
  for (i = 0; i < NUM_DATA; i++)
    data[i] = data2[i] = (std::rand() % range) - (range >> 1);

  std::cout << "Unsorted original data: " << std::endl;
  show_data(data, NUM_DATA);
  std::clock_t start = std::clock();
  shell_sort(data, NUM_DATA);
  std::clock_t end = std::clock();

  std::cout << std::endl
            << "Data Sorted using custom implementation: " << std::endl;
  show_data(data, NUM_DATA);

  double elapsed_time = (end - start) * 1.f / CLOCKS_PER_SEC;
  std::cout << "Time spent sorting: " << elapsed_time << "s\n" << std::endl;

  start = std::clock();
  qsort(data2, NUM_DATA, sizeof(data2[0]), compare);
  end = std::clock();
  std::cout << "Data Sorted using cstdlib qsort: " << std::endl;
  show_data(data2, NUM_DATA);

  elapsed_time = (end - start) * 1.f / CLOCKS_PER_SEC;
  std::cout << "Time spent sorting: " << elapsed_time << "s\n" << std::endl;

  free(data);
  free(data2);
  return 0;
}