Sorting: Quick Sort

Quick sort is a divide and conquer approach to sorting just like Merge sort, however this method is more efficient but it does take up more memory space.
The method divides a list of integers, picks an integer of an array to be a pivot, then moves the integers that are larger in value and moves it to the right of the pivot, and then does that to the smaller ones.

Quick Sort
Algorithm:

public class MyQuickSort {

     

    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) {

            /**

             * In each iteration, we will identify a number from left side which

             * is greater then the pivot value, and also we will identify a number

             * from right side which is less then the pivot value. Once the search

             * is done, then we exchange both numbers.

             */

            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[]){

         

        MyQuickSort sorter = new MyQuickSort();

        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(" ");

        }

    }

}