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C++ Program for ShellSort
• Last Updated : 09 May, 2019

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.

 `// 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
```

Please refer complete article on ShellSort for more details!

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