Heap Sort in Java

Author: Deepali-Srivastava

sorting/HeapSort.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 HeapSort 
+{
+	private HeapSort(){} //this class is not for instantiation
+		
+	public static void sort(int[] a, int n)  
+	{
+		buildHeap_BottomUp(a,n);
+
+		int maxValue;
+		while(n>1)
+		{
+			maxValue=a[1];
+			a[1]=a[n];
+			a[n]=maxValue;
+			n--;  
+	    	restoreDown(1,a,n);
+	    }
+	}
+	
+	public static void buildHeap_BottomUp(int[] arr, int n)
+    {
+    	int i;
+    	for(i=n/2; i>=1; i--)
+    		restoreDown(i,arr,n);
+    }
+	
+	private static void restoreDown(int i, int[] a, int n)
+    {
+    	int k=a[i];
+    	int lchild=2*i, rchild=lchild+1;
+    		
+    	while(rchild<=n)
+    	{
+    		if( k>=a[lchild] && k>=a[rchild] )  
+    		{
+    			a[i]=k;
+    			return;
+    		}
+    		else if(a[lchild] > a[rchild])
+    		{
+    			a[i]=a[lchild]; 
+    			i=lchild;
+    		}
+   		else
+    		{
+    			a[i]=a[rchild];
+    			i=rchild;
+    		}
+    		lchild=2*i;
+    		rchild=lchild+1;
+    	}
+
+    	/*If number of nodes is even*/	
+    	if(lchild==n && k<a[lchild]) 
+    	{
+    		a[i]=a[lchild];
+    		i=lchild;
+    	}
+    	a[i]=k;
+    }
+	
+	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=1; i<=n; i++)
+		{
+			System.out.print("Enter element " + i + " : ");
+			a[i] = scan.nextInt();
+		}
+		
+		sort(a,n);
+		
+		System.out.println("Sorted array is : ");
+		for(i=1; i<=n; i++)
+			System.out.print(a[i] + " ");
+		System.out.println();
+	}
+}
+