Quicksort is a divide and conquer algorithm. It first divides a large list into two smaller sub-lists and then recursively sort the two sub-lists. If we want to sort an array without any extra space, quicksort is a good option. On average, time complexity is O(n log(n)). The basic step of sorting an array are as follows: - Select a pivot, normal…

quick_sort.java

public class QuickSort {
	public static void main(String[] args) {
		int[] x = { 9, 2, 4, 7, 3, 7, 10 };
		System.out.println(Arrays.toString(x));
 
		int low = 0;
		int high = x.length - 1;
 
		quickSort(x, low, high);
		System.out.println(Arrays.toString(x));
	}
 
	public static void quickSort(int[] arr, int low, int high) {
		if (arr == null || arr.length == 0)
			return;
 
		if (low >= high)
			return;
 
		// pick the pivot
		int middle = low + (high - low) / 2;
		int pivot = arr[middle];
 
		// make left < pivot and right > pivot
		int i = low, j = high;
		while (i <= j) {
			while (arr[i] < pivot) {
				i++;
			}
 
			while (arr[j] > pivot) {
				j--;
			}
 
			if (i <= j) {
				int temp = arr[i];
				arr[i] = arr[j];
				arr[j] = temp;
				i++;
				j--;
			}
		}
 
		// recursively sort two sub parts
		if (low < j)
			quickSort(arr, low, j);
 
		if (high > i)
			quickSort(arr, i, high);
	}
}