Java Program to find the intersection of two arrays

    Intersection provides the common elements between two arrays. Let us find the intersection between two arrays in java.

It has two types

1. 1.      Using HashSet
2. 2.      Using Sorted Arrays

Both of the methods are implemented as follows.

1.Using HashSet

              This method implementation uses HashSet objects.

• A public class is created with main() function.
• HashSet objects set1, is1 are created.
• Two arrays are created in the main() function and passed to findIt() function.
• ‘findIt()’ reads the arrays and store it to set1.
• Check the  the second array elements with set1. If both are equal, it is stored in is1.
• Other wise, the loop is moving to next element.
• Finally, the result is displayed.

Program:

import java.util.HashSet;

import java.util.Set;

public class ArrayIsEg {

    public static void findIt(int[] a1, int[] a2) {

        Set<Integer> set1 = new HashSet<>();

        Set<Integer> is1 = new HashSet<>();

        // Let us insert elements of first array to the set

        for (int no : a1) {

            set1.add(no);

        }

        // let us find if there is any common elements

        for (int no : a2) {

            if (set1.contains(no)) {

                is1.add(no);

            }

        }

        // The common elements are displayed here

        System.out.println("Intersection of Arrays: " + is1);

    }

    public static void main(String[] args) {

        int[] a1 = {11, 22, 33, 44, 55};

        int[] a2 = {44, 55, 16, 77};

        findIt(a1, a2);

    }

}

Output:

C:\raji\blog>javac ArrayIsEg.java

C:\raji\blog>java ArrayIsEg

Intersection of Arrays: [55, 44]

2.Using Sorted Arrays

              This method reads two arrays as input and pass it to ‘findIt()’ method.

• ‘findIt()’ method sorts both of array.
• Both of the arrays are compared, if any common elements are there, it prints the element.
• Otherwise, it moves to next element.

Program:

import java.util.Arrays;

public class SortedArrayIs {

    public static void findIt(int[] a1, int[] a2) {

        Arrays.sort(a1);

        Arrays.sort(a2);

        int i = 0, j = 0;

        System.out.print("Intersection of Arrays: ");

        while (i < a1.length && j < a2.length) {

            if (a1[i] == a2[j]) {

                System.out.print(a1[i] + " ");

                i++;

                j++;

            } else if (a1[i] < a2[j]) {

                i++;

            } else {

                j++;

            }

        }

    }

    public static void main(String[] args) {

        int[] a1 = {11, 21, 31, 41, 51};

        int[] a2 = {31, 41, 51, 61, 71};

        findIt(a1, a2);

    }

}

Output:

C:\raji\blog>javac SortedArrayIs.java

C:\raji\blog>java SortedArrayIs

Intersection of Arrays: 31 41 51

This is the way of implementing the intersection of two arrays in java. Hope, this code is useful to you.  Keep Coding!!!