import java.util.Arrays;

public class QuickSort
{
    /* -------------------------------------------------------
       QuickSort: A[s.. e-1]
        ------------------------------------------------------ */
    public static <T extends Comparable<T>> void sort(T[] A, int s, int e)
    {
        if ( e - s <= 1 )       // Base case
            return;             // No need to sort an array of 1 element...

        // Partition A using A[s] as pivot
        int pivotLoc = partition(A, s, e);

        sort(A, s, pivotLoc);   // Sort left  half with quick sort
        sort(A, pivotLoc+1, e); // Sort right half with quick sort
    }


    /* --------------------------------------------------------
       Input:  A[lo] .... A[hi-1]
                 ^
		 |
	       pivot

       Output: Partition A[s] ... A[e-1] so that:
	       pivot = A[s]

               |  values < pivot     | A[s] | values > A[lo] |
                                         ^
					 |
				      index k
       Returns: k
       --------------------------------------------------------- */
    public static <T extends Comparable<T>> int partition(T[] A, int s, int e) 
    {
	T pivot = A[s];
	
        int low = s+1, high = e-1;

	System.out.println("\npartition(A," + s + "," + e +"):");
	System.out.print("Index --> ");
        for ( int k = 0; k < A.length; k++)
            System.out.print( k + "  ");
	System.out.println();

        while (low <= high) 
        {
	    // Show progress
	    System.out.print(">>>>     " + Arrays.toString(A));
	    System.out.print("   Pivot = " + pivot 
			+ " low = " + low + " high = " + high);

	    if ( A[high].compareTo(pivot) >= 0 )
            {
                System.out.println(" -- A[" + high + "] >= " + pivot);
		high--;
            }
	    else
	    {
                System.out.println(" ++ A[" + high + "] <  " + pivot
				 + (low==high ? " ##" : "") );
		exch(A, low, high);
		low++;
	    }

        }

	// Show progress
	System.out.print(">>>>     " + Arrays.toString(A));
	System.out.print("   Pivot = " + pivot 
			+ " low = " + low + " high = " + high);
        System.out.println(" ** exch pivot A[" + s + "] and A[" + high + "]");

	exch(A, s, high);

	System.out.print("Output:  " + Arrays.toString(A));
        System.out.println("\n");

	return high;
    }

    public static <T extends Comparable<T>> void exch(T[] A, int i, int j)
    {
        T h = A[i];
	A[i] = A[j];
	A[j] = h;
    }
}