# Java Program for Iterative Quick Sort

• Last Updated : 13 Jun, 2022

## Java

 `// Java implementation of iterative quick sort``class` `IterativeQuickSort {`` ``void` `swap(``int` `arr[], ``int` `i, ``int` `j)`` ``{``  ``int` `t = arr[i];``  ``arr[i] = arr[j];``  ``arr[j] = 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] and arr[j]``    ``swap(arr, i, j);``   ``}``  ``}``  ``// swap arr[i+1] and arr[h]``  ``swap(arr, i + ``1``, h);``  ``return` `(i + ``1``);`` ``}` ` ``// Sorts arr[l..h] using iterative QuickSort`` ``void` `QuickSort(``int` `arr[], ``int` `l, ``int` `h)`` ``{``  ``// create auxiliary stack``  ``int` `stack[] = ``new` `int``[h - l + ``1``];` `  ``// initialize top of stack``  ``int` `top = -``1``;` `  ``// push initial values in the stack``  ``stack[++top] = l;``  ``stack[++top] = h;` `  ``// keep popping elements until stack is not empty``  ``while` `(top >= ``0``) {``   ``// pop h and l``   ``h = stack[top--];``   ``l = stack[top--];` `   ``// set pivot element at it's proper position``   ``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)``   ``System.out.print(arr[i] + ``" "``);`` ``}` ` ``// Driver code to test above`` ``public` `static` `void` `main(String args[])`` ``{``  ``IterativeQuickSort ob = ``new` `IterativeQuickSort();``  ``int` `arr[] = { ``4``, ``3``, ``5``, ``2``, ``1``, ``3``, ``2``, ``3` `};``  ``ob.QuickSort(arr, ``0``, arr.length - ``1``);``  ``ob.printArr(arr, arr.length);`` ``}``}``/*This code is contributed by Rajat Mishra */`

Output:

`1 2 2 3 3 3 4 5`

Time Complexity: O(n*log(n))
Auxiliary Space: O(n)

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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