C++ Program for ShellSort

In shellSort, we make the array h-sorted for a large value of h. We keep reducing the value of h until it becomes 1. An array is said to be h-sorted if all sublists of every h'th element is sorted. 

CPP

// C++ implementation of Shell Sort 
#include <iostream> 

/* function to sort arr using shellSort */
void shellSort(int arr[], int n) 
{ 
 // Start with a big gap, then reduce the gap 
 for (int gap = n / 2; gap > 0; gap /= 2) { 
  // Do a gapped insertion sort for this gap size. 
  // The first gap elements arr[0..gap-1] are already in gapped order 
  // keep adding one more element until the entire array is 
  // gap sorted 
  for (int i = gap; i < n; i += 1) { 
   // add arr[i] to the elements that have been gap sorted 
   // save arr[i] in temp and make a hole at position i 
   int temp = arr[i]; 

   // shift earlier gap-sorted elements up until the correct 
   // location for arr[i] is found 
   int j; 
   for (j = i; j >= gap && arr[j - gap] > temp; j -= gap) 
    arr[j] = arr[j - gap]; 

   // put temp (the original arr[i]) in its correct location 
   arr[j] = temp; 
  } 
 } 
} 

void printArray(int arr[], int n) 
{ 
 for (int i = 0; i < n; i++) 
  std::cout << arr[i] << " "; 
 std::cout << "\n"; 
} 

int main() 
{ 
 int arr[] = { 12, 34, 54, 2, 3 }; 
 int n = sizeof(arr) / sizeof(arr[0]); 

 std::cout << "Array before sorting: \n"; 
 printArray(arr, n); 

 shellSort(arr, n); 

 std::cout << "Array after sorting: \n"; 
 printArray(arr, n); 
} 

Output:

Array before sorting: 
12 34 54 2 3 
Array after sorting: 
2 3 12 34 54

Time Complexity: O(n²)
Auxiliary Space: O(1)

Please refer complete article on ShellSort for more details!

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