Program to perform Quick Sort.

Code:

public class QuickSort
{    
    private int array[];
    private int length;
    public void sort(int[] inputArr)
    {        
        if (inputArr == null || inputArr.length == 0)
        {
            return;
        }
        this.array = inputArr;
        length = inputArr.length;
        quickSort(0, length - 1);
    }

    private void quickSort(int lowerIndex, int higherIndex)
    {    
        int i = lowerIndex;
        int j = higherIndex;
        // calculate pivot number, I am taking pivot as middle index number
        int pivot = array[lowerIndex+(higherIndex-lowerIndex)/2];
        // Divide into two arrays
        while (i <= j)
        {        
            while (array[i] < pivot)
            {
                i++;
            }
            while (array[j] > pivot)
            {
                j--;
            }
            if (i <= j)
            {
                exchangeNumbers(i, j);
                //move index to next position on both sides
                i++;
                j--;
            }
        }
        // call quickSort() method recursively
        if (lowerIndex < j)
            quickSort(lowerIndex, j);
        if (i < higherIndex)
            quickSort(i, higherIndex);
    }

    private void exchangeNumbers(int i, int j)
    {
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
    
    public static void main(String a[])
    {        
        QuickSort sorter = new QuickSort();
        int[] input = {24,2,45,20,56,75,2,56,99,53,12};
        sorter.sort(input);
        for(int i:input)
        {
            System.out.print(i);
            System.out.print(" ");
        }
    }
}