In Java How to Find Common Elements of Two UnSorted Array?

How to Find Common Elements of Two UnSorted Array? Below is a simple Java Code which shows it.

Steps:

• Find 1st small array.
• Iterate through small array and find elements in largest array.
• In case of match, add it to separate new array.
• Display final array.

Approach-1:

package com.crunchify;

import java.util.HashSet;

/**
 * @author Crunchify.com
 */

public class CrunchifyIntersection {

	public static void main(String[] args) {
        Integer[ ] arrayOne = { 1, 4, 5, 2, 7, 3, 9 };
        Integer[ ] arrayTwo = { 5, 2, 4, 9, 5 };

        Integer[ ] common = CrunchifyIntersection.findCommon( arrayOne, arrayTwo );

        System.out.print( "Common Elements Between Two Arrays: " );       
        for( Integer entry : common ) {
            System.out.print( entry + " " );
        }
	}
	   public static Integer[ ] findCommon( Integer[ ] arrayOne, Integer[ ] arrayTwo ) {

	    	Integer[ ] arrayToHash;
	    	Integer[ ] arrayToSearch;

	    	if( arrayOne.length < arrayTwo.length ) {
	    		arrayToHash = arrayOne;
	    		arrayToSearch = arrayTwo;
	    	} else {
	    		arrayToHash = arrayTwo;
	    		arrayToSearch = arrayOne;
	    	}

	        HashSet<Integer> intersection = new HashSet<Integer>( );

	        HashSet<Integer> hashedArray = new HashSet<Integer>( );
	        for( Integer entry : arrayToHash ) {
	            hashedArray.add( entry );
	        }

	        for( Integer entry : arrayToSearch ) {
	            if( hashedArray.contains( entry ) ) {
	                intersection.add( entry );
	            }
	        }

	        return intersection.toArray( new Integer[ 0 ] );
	    }
}

Output:

Common Elements Between Two Arrays: 2 4 5 9

---

Approach-2

Below approach is suggested by our reader Maksudur rahman as you see it in below comment section. Please find here complete example.

package crunchify.com.tutorials;

import java.util.Arrays;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * @author Crunchify.com
 * 
 */

public class CrunchifyIntersection {

	public static void main(String[] args) {
		Integer[] arrayOne = { 1, 4, 5, 2, 7, 3, 9 };
		Integer[] arrayTwo = { 5, 2, 4, 9, 5 };

		Set<Integer> crunchifySet1 = new LinkedHashSet<Integer>(Arrays.asList(arrayOne));
		Set<Integer> crunchifySet2 = new LinkedHashSet<Integer>(Arrays.asList(arrayTwo));

		for (Integer crunchify : crunchifySet2) {
			if (!crunchifySet1.add(crunchify)) {
				System.out.println("The duplicate element of an Array is " + crunchify);
			}
		}
	}
}

Output:

The duplicate element of an Array is 5
The duplicate element of an Array is 2
The duplicate element of an Array is 4
The duplicate element of an Array is 9