Exercise_5.java

import java.util.Stack;
//time - O(n log n)
// space - O(log n )
class IterativeQuickSort {
    void swap(int arr[], int i, int j) 
    { 
	//Try swapping without extra variable
        if (i == j) return;
        arr[i] = arr[i]^arr[j];
        arr[j] = arr[i]^arr[j];
        arr[i] = arr[i]^arr[j];
    } 
  
    /* This function is same in both iterative and 
       recursive*/
    int partition(int arr[], int l, int h) 
    { 
        int pivot = arr[h];
        int i = (l - 1);
        for (int j = l; j < h; j++){
            if (arr[j] <= pivot){
                i++;
                swap(arr, i, j);
            }
        }
        swap(arr, i + 1, h);

        return i+1;
    }
  
    // Sorts arr[l..h] using iterative QuickSort 
    void QuickSort(int arr[], int l, int h) 
    { 
        //Try using Stack Data Structure to remove recursion.
        Stack<int[]> stack = new Stack<>();
        stack.push(new int[]{l,h});

        while (!stack.isEmpty()){
            int[] temp = stack.pop();
            l = temp[0];
            h = temp[1];
            if(l < h){
                int pi = partition(arr, l, h);
                stack.push(new int[]{l,pi-1});
                stack.push(new int[]{pi+1, 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); 
    } 
}