files renamed to standard - without spaces and made CPPLINT compatible

sorting/shell_sort2.cpp

@@ -0,0 +1,105 @@
+#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;
+}