Case-1 : Dividing two arrays in one

• Both Arrays have to be sorted, in order to implement this case.

• Comparing two arrays of element, smallest will occupy in new array.

• Time Complexity is O(N^2)

  public class Main
  {
  	public static void main(String[] args) {
      int[] arr1 = new int[]{1,5,9}; //Array-1
      int[] arr2 = new int[]{2,3,10}; // Array-2
      int m = arr1.length;
      int n = arr2.length;
      int[] arr3 = new int[m+n]; //Array-3
      int i=0,j=0,k=0;
      while(i<m && j<n)
      {
          if(arr1[i]<arr2[j]) //Comparing two arrays in-order to insert in array-3.
          {
              arr3[k] = arr1[i];
              i++;
              k++;
          }
          else{
              arr3[k] = arr2[j];
              k++;
              j++;
          }
      }//By the end of the loop any one of two array is sorted if the elements left in any array we have to add while loop
      while(i<m) 
      {
          arr3[k] = arr1[i];
          k++;
          i++;
      }
      while(j<n)
      {
          arr3[k] = arr2[j];
          j++;
          k++;
      }
      //All Elements are added to the array-3.
      for(int l=0;l<arr3.length;l++)
      {
          System.out.println(arr3[l]); //Printing the values of array-3.
      }
  	}
  }
  

Case -2 : Merging array in one array using one array.

										// C program to implement merge sort
#include <stdio.h>
#include <stdlib.h>
void mergesort(int[],int,int);
void merge(int[],int,int,int);
int main() {
    int a[10],n;
    printf("Enter number of elements inside array :\\n");
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        printf("Enter element %d : \\n",i);
        scanf("%d",&a[i]);
    }
    mergesort(a,0,n-1);
    printf("\\n Sorted Array is : \\n");
    for(int i=0;i<n;i++)
    {
        printf("%d\\n",a[i]);
    }
    return 0;
}
void mergesort(int a[],int low,int high)
{
    int mid;
    if(low<high){
        mid=(low+high)/2;
        mergesort(a,low,mid);
        mergesort(a,mid+1,high);
        merge(a,low,mid,high);
    }
}
void merge(int a[],int low,int mid,int high)
{
    int i,j,k,b[20];
    i=low;
    k=low;
    j=mid+1;//3,5,6|4,2,6
    while(i<=mid && j<=high)
    {
        if(a[i]<a[j])
        {
            b[k]=a[i];
            i++;
            k++;
        }
        else{
            b[k]=a[j];
            j++;
            k++;
        }
    }
    while(i<=mid)
    {
        b[k]=a[i];
        i++;
        k++;
    }
    while(j<=high)
    {
        b[k]=a[j];
        j++;
        k++;
    }
    for(int i=low;i<=high;i++)
    {
        a[i]=b[i];
    }
}

/* Java program for Merge Sort */
class MergeSort
{
	// Merges two subarrays of arr[].
	// First subarray is arr[l..m]
	// Second subarray is arr[m+1..r]
	void merge(int arr[], int l, int m, int r)
	{
		// Find sizes of two subarrays to be merged
		int n1 = m - l + 1;
		int n2 = r - m;

		/* Create temp arrays */
		int L[] = new int [n1];
		int R[] = new int [n2];

		/*Copy data to temp arrays*/
		for (int i=0; i<n1; ++i)
			L[i] = arr[l + i];
		for (int j=0; j<n2; ++j)
			R[j] = arr[m + 1+ j];

		/* Merge the temp arrays */

		// Initial indexes of first and second subarrays
		int i = 0, j = 0;

		// Initial index of merged subarray array
		int k = l;
		while (i < n1 && j < n2)
		{
			if (L[i] <= R[j])
			{
				arr[k] = L[i];
				i++;
			}
			else
			{
				arr[k] = R[j];
				j++;
			}
			k++;
		}

		/* Copy remaining elements of L[] if any */
		while (i < n1)
		{
			arr[k] = L[i];
			i++;
			k++;
		}

		/* Copy remaining elements of R[] if any */
		while (j < n2)
		{
			arr[k] = R[j];
			j++;
			k++;
		}
	}

	// Main function that sorts arr[l..r] using
	// merge()
	void sort(int arr[], int l, int r)
	{
		if (l < r)
		{
			// Find the middle point
			int m = (l+r)/2;

			// Sort first and second halves
			sort(arr, l, m);
			sort(arr , m+1, r);

			// Merge the sorted halves
			merge(arr, l, m, r);
		}
	}

	/* A utility function to print array of size n */
	static void printArray(int arr[])
	{
		int n = arr.length;
		for (int i=0; i<n; ++i)
			System.out.print(arr[i] + " ");
		System.out.println();
	}

	// Driver method
	public static void main(String args[])
	{
		int arr[] = {12, 11, 13, 5, 6, 7};

		System.out.println("Given Array");
		printArray(arr);

		MergeSort ob = new MergeSort();
		ob.sort(arr, 0, arr.length-1);

		System.out.println("\\nSorted array");
		printArray(arr);
	}
}