Find common elements among two unsorted arrays

Sometimes, you may face this situation that you have 2 arrays and both are unsorted. You need to compare them and find out the common values. How to find out common elements in 2 unsorted arrays?

Suppose, you are extracting data from Database as well as from front end Application. Now, you need to compare the data extracted from both the sources.Let’s see with an example.

In the example below, we have 2 Integer arrays which are having some values. There are following steps which you will perform to complete the job.

Steps:

• Compare the length of both the array and find the small one.
• Iterate through small array and put unique values in a HashSet.
• Iterate through large array and find the elements stored in the previous Hashset.
• If find common value, add to a new array.
• Display final array.

package com.array;

import java.util.HashSet;

public class CommonValUnsortedArray {

	public static void main(String[] args) {
		
		Integer[ ] arrayFirst = { 4,3,7,2,4,0,8,2,5};
        Integer[ ] arraySecond = { 9,5,9,4,1};
 
        Integer[ ] commonValues = CommonValUnsortedArray.findCommonValues( arrayFirst, arraySecond );
 
        System.out.print( "Common Elements Between Two Arrays: " );       
        for( Integer vaule : commonValues ) {
            System.out.print( vaule + " " );   //Display the common values 
        }

	}
	
	
	public static Integer[ ] findCommonValues( Integer[ ] arrayFirst, Integer[ ] arraySecond ) {
		 
    	Integer[ ] arrStoreCommon;
    	Integer[ ] arrayToSearch;

    	if( arrayFirst.length < arraySecond.length ) {
    		arrStoreCommon = arrayFirst;
    		arrayToSearch = arraySecond;
    	} else {
    		arrStoreCommon = arraySecond;
    		arrayToSearch = arrayFirst;
    	}

        HashSet<Integer> newArray = new HashSet<Integer>( );
        HashSet<Integer> hashedArray = new HashSet<Integer>( );
        
        //It will add only unique values into the HashSet
        for( Integer value : arrStoreCommon ) {
            hashedArray.add(value);
        }
         
        //Check into another array , if value matches then add those values into a new HashSet
        for( Integer value : arrayToSearch ) {
            if( hashedArray.contains(value) ) {
            	newArray.add(value);
            }
        }

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

}

Output: