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C Program for Iterative Quick Sort
• Last Updated : 04 Dec, 2018
 `// An iterative implementation of quick sort``#include `` ` `// A utility function to swap two elements``void` `swap(``int``* a, ``int``* b)``{``    ``int` `t = *a;``    ``*a = *b;``    ``*b = t;``}`` ` `/* This function is same in both iterative and recursive*/``int` `partition(``int` `arr[], ``int` `l, ``int` `h)``{``    ``int` `x = arr[h];``    ``int` `i = (l - 1);`` ` `    ``for` `(``int` `j = l; j <= h - 1; j++) {``        ``if` `(arr[j] <= x) {``            ``i++;``            ``swap(&arr[i], &arr[j]);``        ``}``    ``}``    ``swap(&arr[i + 1], &arr[h]);``    ``return` `(i + 1);``}`` ` `/* A[] --> Array to be sorted, ``   ``l  --> Starting index, ``   ``h  --> Ending index */``void` `quickSortIterative(``int` `arr[], ``int` `l, ``int` `h)``{``    ``// Create an auxiliary stack``    ``int` `stack[h - l + 1];`` ` `    ``// initialize top of stack``    ``int` `top = -1;`` ` `    ``// push initial values of l and h to stack``    ``stack[++top] = l;``    ``stack[++top] = h;`` ` `    ``// Keep popping from stack while is not empty``    ``while` `(top >= 0) {``        ``// Pop h and l``        ``h = stack[top--];``        ``l = stack[top--];`` ` `        ``// Set pivot element at its correct position``        ``// in sorted array``        ``int` `p = partition(arr, l, h);`` ` `        ``// If there are elements on left side of pivot,``        ``// then push left side to stack``        ``if` `(p - 1 > l) {``            ``stack[++top] = l;``            ``stack[++top] = p - 1;``        ``}`` ` `        ``// If there are elements on right side of pivot,``        ``// then push right side to stack``        ``if` `(p + 1 < h) {``            ``stack[++top] = p + 1;``            ``stack[++top] = h;``        ``}``    ``}``}`` ` `// A utility function to print contents of arr``void` `printArr(``int` `arr[], ``int` `n)``{``    ``int` `i;``    ``for` `(i = 0; i < n; ++i)``        ``printf``(``"%d "``, arr[i]);``}`` ` `// Driver program to test above functions``int` `main()``{``    ``int` `arr[] = { 4, 3, 5, 2, 1, 3, 2, 3 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(*arr);``    ``quickSortIterative(arr, 0, n - 1);``    ``printArr(arr, n);``    ``return` `0;``}`
Output:
```1 2 2 3 3 3 4 5
```

The above mentioned optimizations for recursive quick sort can also be applied to iterative version.

1) Partition process is same in both recursive and iterative. The same techniques to choose optimal pivot can also be applied to iterative version.

2) To reduce the stack size, first push the indexes of smaller half.

3) Use insertion sort when the size reduces below a experimentally calculated threshold.

Please refer complete article on Iterative Quick Sort for more details!

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