Merge Sort in Java

Author: Deepali-Srivastava

sorting/MergeSortIterative.java

@@ -0,0 +1,101 @@
+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+import java.util.Scanner;
+
+
+public class MergeSortIterative 
+{
+	public static void sort(int a[], int n)
+	{
+		int[] temp = new int[n];
+		int size=1;
+		while(size<=n-1)
+		{
+			sortPass(a,temp,size,n);
+			size=size*2;
+		}
+	}
+
+	private static void sortPass(int a[], int temp[], int size, int n)
+	{
+		int i,low1,up1,low2,up2;
+		
+		low1=0;
+		
+		while( low1+size <= n-1 )
+		{
+			up1=low1+size-1;
+			low2=low1+size;
+			up2=low2+size-1;
+			
+			if(up2>=n)/*if length of last sublist is less than size*/ 						
+				up2=n-1;
+			
+			merge(a,temp,low1,up1,low2,up2);
+			
+			low1=up2+1;	/*Take next two sublists for merging*/
+		}
+		
+		for(i=low1; i<=n-1; i++)
+			temp[i]=a[i];	/*If any sublist is left alone*/
+		
+		copy(a, temp, n); 
+	}
+
+	
+	/* a[low1]...a[up1] and a[low2]...a[up2] merged to temp[low1]...temp[up2] */
+	private static void merge( int a[], int temp[], int low1, int up1, int low2, int up2 )
+	{
+		int i = low1;
+		int j = low2;
+		int k = low1;
+
+		while( (i<=up1) && (j<=up2) )
+		{
+			if(a[i]<=a[j])
+				temp[k++]=a[i++];
+			else
+				temp[k++]=a[j++];
+		}
+
+		while(i<=up1)
+			temp[k++]=a[i++];
+		
+		while(j<=up2)
+			temp[k++]=a[j++];
+	}
+	
+	/*copies temp[low]....temp[up] to a[low]...a[up]*/
+	private static void copy(int a[], int temp[], int n)
+	{
+		for(int i=0; i<n; i++)
+			a[i]=temp[i];
+	}
+
+	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();
+	}
+}

sorting/MergeSortRecursive.java

@@ -0,0 +1,87 @@
+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+import java.util.Scanner;
+
+public class MergeSortRecursive 
+{
+	private MergeSortRecursive(){} //this class is not for instantiation
+	
+	public static void sort(int a[], int n)
+	{
+		int[] temp = new int[n];
+		sort(a,temp,0,n-1);
+	}
+	
+	private static void sort(int[] a, int[] temp, int low, int up)
+	{
+		if(low==up) /*only one element*/
+			return;
+
+		int mid = (low+up)/2;
+			
+		sort(a, temp, low, mid);  /* Sort a[low]....a[mid] */
+		sort(a, temp, mid+1, up);  /* Sort a[mid+1]....a[up] */
+			
+		/* Merge a[low]...a[mid] and a[mid+1]....a[up] to temp[low]...temp[up] */
+		merge(a, temp, low, mid, mid+1, up); 
+		
+		/* Copy temp[low]...temp[up] to a[low]...a[up] */ 
+		copy(a,temp,low,up);	
+	}
+	
+	/* a[low1]...a[up1] and a[low2]...a[up2] merged to temp[low1]...temp[up2] */
+	private static void merge( int a[], int temp[], int low1, int up1, int low2, int up2 )
+	{
+		int i = low1;
+		int j = low2;
+		int k = low1;
+
+		while( (i<=up1) && (j<=up2) )
+		{
+			if(a[i]<=a[j])
+				temp[k++]=a[i++];
+			else
+				temp[k++]=a[j++];
+		}
+
+		while(i<=up1)
+			temp[k++]=a[i++];
+		
+		while(j<=up2)
+			temp[k++]=a[j++];
+	}
+
+	/*copies temp[low]....temp[up] to a[low]...a[up]*/
+	private static void copy(int[] a, int[] temp, int low, int up)
+	{
+		for(int i=low; i<=up; i++)
+			a[i]=temp[i];
+	}
+
+	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();
+	}
+}