Java Array Programs

Here are the different methods of finding the missing and duplicate numbers between two arrays. If you want to check out more Java programs, you can follow this link.

Find the Missing and Duplicate Numbers in the Array

1. UsingTemp Variable

package com.softwaretestingo.interviewprograms;
public class FindMissingDuplicateNumberEX1 
{
	static void printTwoElements(int[] arr, int n)
    {
        int[] temp = new int[n]; // Creating temp array of size n
        
        // with initial values as 0.
        int repeatingNumber = -1;
        int missingNumber = -1;
 
        for (int i = 0; i < n; i++) 
        {
            temp[arr[i] - 1]++;
            if (temp[arr[i] - 1] > 1) 
            {
                repeatingNumber = arr[i];
            }
        }
        for (int i = 0; i < n; i++) 
        {
            if (temp[i] == 0) 
            {
                missingNumber = i + 1;
                break;
            }
        }
 
        System.out.println("The repeating number is " + repeatingNumber + ".");
        System.out.println("The missing number is " + missingNumber + ".");
    }

	public static void main(String[] args) 
	{
		int[] arr = { 7, 3, 4, 5, 5, 6, 2 };
        int n = arr.length;
        printTwoElements(arr, n);
	}
}

2. Next Way

package com.softwaretestingo.interviewprograms;

public class FindMissingDuplicateNumberEX2 
{
	static void printTwoElements(int arr[], int size)
    {
        int i;
        System.out.print("The repeating element is ");
 
        for (i = 0; i < size; i++) 
        {
            int abs_val = Math.abs(arr[i]);
            if (arr[abs_val - 1] > 0)
                arr[abs_val - 1] = -arr[abs_val - 1];
            else
                System.out.println(abs_val);
        }
 
        System.out.print("and the missing element is ");
        for (i = 0; i < size; i++) 
        {
            if (arr[i] > 0)
                System.out.println(i + 1);
        }
    }

	public static void main(String[] args) 
	{
		int arr[] = { 7, 3, 4, 5, 5, 6, 2 };
        int n = arr.length;
        printTwoElements(arr, n);
	}
}

3. Using Map

package com.softwaretestingo.interviewprograms;
import java.util.HashMap;
import java.util.Map;
public class FindMissingDuplicateNumberEX3 
{
	public static void main(String[] args) 
	{
		int[] arr = { 4, 3, 6, 2, 1, 1, 2 };

		Map<Integer, Boolean> numberMap = new HashMap<>();

		int max = arr.length;
		
		for (Integer i : arr) 
		{

			if (numberMap.get(i) == null) 
			{
				numberMap.put(i, true);
			}
			else 
			{
				System.out.println("Repeating = " + i);
			}
		}
		for (int i = 1; i <= max; i++)
		{
			if (numberMap.get(i) == null) 
			{
				System.out.println("Missing = " + i);
			}
		}
	}
}

Now We will try to Find the missing number between two Arrays.

package com.softwaretestingo.interviewprograms;
import java.util.Arrays;
public class FindMissingNumberBetween2ArrayEx 
{
	private static int missingNumber(int[] arr1, int arr2[]) 
	{
		 
        int missingNumber = arr1[0];
        for (int index = 1; index < arr1.length; index++) 
        {
            missingNumber ^= arr1[index];
        }
 
        for (int index = 0; index < arr2.length; index++) 
        {
            missingNumber ^= arr2[index];
        }
        return missingNumber;
    }
	public static void main(String[] args) 
	{
		int array1[] = { 1, 2, 3, 4, 5 };
        int array2[] = { 1, 2, 4, 5 };
 
        String sArr1 = Arrays.toString(array1);
        String sArr2 = Arrays.toString(array2);
 
        System.out.printf("1. Missing number in array1 & array2 is:", sArr1, sArr2);
        int missingNumber = missingNumber(array1, array2);
        System.out.printf(" %d", missingNumber);
 
        array1 = new int[] { 10, 20, 30, 40 };
        array2 = new int[] { 20, 30, 40,  };
 
        sArr1 = Arrays.toString(array1);
        sArr2 = Arrays.toString(array2);
 
        System.out.printf("\n2. Missing number in array1 & array2 is:", sArr1, sArr2);
        missingNumber = missingNumber(array1, array2);
        System.out.printf(" %d", missingNumber);
	}
}