Java: Quick sort Algorithm

Last update on April 29 2025 13:10:51 (UTC/GMT +8 hours)

Write a Java program to sort an array of given integers using the Quick sort algorithm.

Quick sort is a comparison sort, meaning it can sort items of any type for which a "less-than" relation (formally, a total order) is defined.

Pictorial presentation - Quick Sort algorithm :

Sample Solution:

Java Code:

import java.util.Arrays;
public class QuickSort {
     
    private int temp_array[];
    private int len;
 
    public void sort(int[] nums) {
         
        if (nums == null || nums.length == 0) {
            return;
        }
        this.temp_array = nums;
        len = nums.length;
        quickSort(0, len - 1);
    }
     private void quickSort(int low_index, int high_index) {
         
        int i = low_index;
        int j = high_index;
        // calculate pivot number 
        int pivot = temp_array[low_index+(high_index-low_index)/2];
        // Divide into two arrays
        while (i <= j) {
               while (temp_array[i] < pivot) {
                i++;
            }
            while (temp_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 (low_index < j)
            quickSort(low_index, j);
        if (i < high_index)
            quickSort(i, high_index);
    }
 
    private void exchangeNumbers(int i, int j) {
        int temp = temp_array[i];
        temp_array[i] = temp_array[j];
        temp_array[j] = temp;
    }
     
     // Method to test above
    public static void main(String args[])
    {
        QuickSort ob = new QuickSort();
        int nums[] = {7, -5, 3, 2, 1, 0, 45};
        System.out.println("Original Array:");
        System.out.println(Arrays.toString(nums));
        ob.sort(nums);
        System.out.println("Sorted Array");
        System.out.println(Arrays.toString(nums));
    }
}

Sample Output:

Original Array:
[7, -5, 3, 2, 1, 0, 45]
Sorted Array
[-5, 0, 1, 2, 3, 7, 45]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to implement quick sort recursively with a randomized pivot selection to avoid worst-case performance.
• Write a Java program to perform quick sort on an array of objects using a custom comparator for descending order.
• Write a Java program to modify quick sort to sort only a portion of the array between given indices.
• Write a Java program to implement quick sort that switches to insertion sort when the subarray size falls below a threshold.

Java Code Editor:

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