Exercise_5.java

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) 
    { 
        //Compare elements and swap.
        int i = l-1;

       for(int j = l; j < h; j++)
       {
            if(arr[j] < arr[h])
            {
                i += 1;
                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[]> st = new Stack<int[]>();
        st.push(new int[] {l,h});

        while(!st.isEmpty())
        {
            int[] boundary = st.pop();
            int low = boundary[0], high = boundary[1];

            if(low<high)
            {
                int pivot = partition(arr, low, high);
                st.push(new int[] {low, pivot - 1});
                st.push(new int[] {pivot + 1, high});
            }
        }
    } 
  
    // 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); 
    } 
}