# C++ Program for ShellSort

• Last Updated : 10 Jun, 2022

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 `   `/* 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); `   ` ``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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