Quick Sort in Java

Published on 28 April 2022 (Updated: 18 September 2022)

Quick Sort in Java

Welcome to the Quick Sort in Java page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

import java.util.ArrayList;

public class QuickSort {

    public static void main(String[] args) {
        ArrayList<Integer> numList=new ArrayList<>();
        if(args.length<1) {
            System.out.println("Usage: please provide a list of at least two integers to sort in the format \"1, 2, 3, 4, 5\"");
        }
        else if(args[0].length()<2) {
            System.out.println("Usage: please provide a list of at least two integers to sort in the format \"1, 2, 3, 4, 5\"");
        }
        else {
            String[] stringList=args[0].split(",");
            if(stringList.length<2) {
                System.out.println("Usage: please provide a list of at least two integers to sort in the format \"1, 2, 3, 4, 5\"");
            }
            else {
            for(int i=0;i<stringList.length;i++) {
                numList.add(Integer.parseInt(stringList[i].trim()));
            }
            if(numList.size()<2) {
                System.out.println("Usage: please provide a list of at least two integers to sort in the format \"1, 2, 3, 4, 5\"");
            }
            else {
                sort(numList,0,numList.size()-1);
                String str="";
                for(int i=0;i<numList.size()-1;i++) {
                    str+=String.valueOf(numList.get(i));
                    str+=", ";
                }
                str+=String.valueOf(numList.get(numList.size()-1));
                System.out.println(str);
            }
         }
        }
    }

    public static int partition(ArrayList<Integer> arr, int low, int high) 
    { 
        int pivot = arr.get(high);  
        int i = (low-1); 
        for (int j=low; j<high; j++) 
        {
            if (arr.get(j) <= pivot) 
            { 
                i++;  
                int temp = arr.get(i); 
                arr.set(i,arr.get(j)); 
                arr.set(j,temp); 
            } 
        } 
        int temp = arr.get(i+1); 
        arr.set(i+1,arr.get(high)); 
        arr.set(high,temp); 
        return i+1; 
    } 

    public static void sort(ArrayList<Integer> arr, int low, int high) 
    { 
        if (low < high) 
        { 
            int pi = partition(arr, low, high); 
            sort(arr, low, pi-1); 
            sort(arr, pi+1, high); 
        } 
    } 
}

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