QuickSort.java

package com.aniketh;

import java.util.Arrays;

public class QuickSort {
    public static void main(String[] args) {
        int[] arr = {5,4,3,2,1};
        sort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }

    static void sort(int[] arr, int low, int high) {
        if (low >= high) {
            return;
        }

        int s = low;
        int e = high;
        int m = s + (e - s) / 2;
        int pivot = arr[m];

        while(s <= e) {
            // also a reason why if it's already sorted it will not swap
            while (arr[s] < pivot) {
                s++;
            }
            while (arr[e] > pivot) {
                e--;
            }
            if (s <= e) {
                int temp = arr[s];
                arr[s] = arr[e];
                arr[e] = temp;

                s++;
                e--;
            }
        }

        // Now my pivot is at correct index, please solve two halves now.
        sort(arr, low, e);
        sort(arr, s, high);
    }
}