Quick Sort in Java

Author: Deepali-Srivastava

sorting/QuickSort.java

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+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+import java.util.Scanner;
+
+public class QuickSort 
+{
+	private QuickSort(){} //this class is not for instantiation
+		
+	public static void sort(int[] a, int n) 
+	{
+		sort(a,0,n-1);
+	}
+	
+	private static void sort(int a[],int low,int up)
+	{
+		if(low>=up) /*zero or one element in sublist*/
+			return;
+		int p = partition(a,low,up);
+		sort(a,low,p-1); /*Sort left sublist*/
+		sort(a,p+1,up);  /*Sort right sublist*/
+	}
+
+	private static int partition(int[] a, int low, int up)
+	{
+		int temp,i,j,pivot;
+		
+		pivot=a[low]; 
+
+		i=low+1; /*moves from left to right*/
+		j=up;    /*moves from right to left*/
+		
+		while(i<=j)  
+		{
+			while( a[i]<pivot && i<up ) 
+	   			i++; 
+			
+			while( a[j] > pivot ) 	
+				j--;
+			
+			if(i<j) /*swap a[i] and a[j]*/
+			{
+				temp=a[i];	
+				a[i]=a[j];	
+				a[j]=temp;
+				i++; 
+				j--;
+			}
+			else /*found proper place for pivot*/
+				break;
+		}
+		
+		/* Proper place for pivot is j */
+		a[low]=a[j];
+		a[j]=pivot;
+		
+		return j;
+	}
+
+	
+	public static void main(String[] args)
+	{
+		int i,n;
+		int[] a = new int[20];
+		Scanner scan = new Scanner(System.in);	
+		
+		System.out.print("Enter the number of elements : ");
+		n = scan.nextInt();
+				
+		for(i=0; i<n; i++)
+		{
+			System.out.print("Enter element " + (i+1) + " : ");
+			a[i] = scan.nextInt();
+		}
+		
+		sort(a,n);
+		
+		System.out.println("Sorted array is : ");
+		for(i=0; i<n; i++)
+			System.out.print(a[i] + " ");
+		System.out.println();
+		scan.close();
+	}
+
+}