#1. Java Program To Check Equality Of Two Arrays

Write a Java program to check if two arrays are equal or not.

If you prefer watching YouTube video for this programming question then you can refer here:-

Whenever programming questions are asked in interviews especially in startups and product-based companies, the interviewer expects you to ask questions to understand problems well instead of directly jumping on writing codes. It may be one of the criteria to evaluate your candidature.

From the above statement, it is not clear if given arrays will be single or multi-dimensional and how equality is defined here. You may ask the below questions:-

Will arrays be single or multidimensional?
Should both arrays contain same elements in same order or same number of elements irrespective of order?

I will consider answers to the above questions below:-

Arrays will be single dimensional.
Both arrays should have same number of elements in the same order.

Even to be more sure you can confirm types of arrays. Just in case of negative scenarios one array may be an int while another String.

The next step is to think about logic. Once you get the logic you can write code.

There are already readymade methods named equals() and deepEquals() provided by class “Arrays” but in interviews, we are not allowed to use these methods.

int[] arr1 = {10,20,30,40};
int[] arr2 = {10,20,30,40};

Let’s take above two int arrays as example. To check equality you might be loooking at elements of both arrays but don’t you think first we should check the equality of lengths of both arrays first as that will be basic entry criteria before we go for further step.
If lengths of arrays are not same then why even we should go and iterate through both arrays to check equality of elements. Lengths of both arrays are not equal means arrays are not equals.
If lengths are matched then we should iterate arrays to match if each indexe has same elements in both arrays.
If at any index, elements are not equal in both arrays then we should terminate the loop then and there as there is no meaning of checking for remaining indexes as we know that both arrays are not equal.

The below flowchart can summerize above logic:-

Now you can write Java code easily implementing above logics.

package arraysprograms;

public class CheckForArrayEquality {

        public static void main(String[] args) {

                int[] arr1 = { 10, 20, 30, 40 };
                int[] arr2 = { 10, 20, 30, 40 };

                // Let's assume both arrays are equal.
                boolean isEqual = true;

                // We need to check length of arrays
                if (arr1.length == arr2.length) {
                        // As lengths of arrays are same, we should iterate arrays now
                        for (int i = 0; i < arr1.length; i++) {
                                // If elements are not equals at any index, set the value false and creak loop
                                if (arr1[i] != arr2[i]) {
                                        isEqual = false;
                                        break;
                                }
                        }
                }
                // Lengths are not same i.e arrays are not equal.
                else
                        isEqual = false;

                if (isEqual)
                        System.out.println("Arrays are equal");
                else
                        System.out.println("Arrays are not equal");

        }

}

For inputs:-
int[] arr1 = { 10, 20, 30, 40 };
int[] arr2 = { 10, 20, 30, 40 };
Arrays are equal

For inputs:-
int[] arr1 = { 10, 20, 30, 40 };
int[] arr2 = { 10, 200, 30, 40 };
Arrays are not equal

For inputs:-
int[] arr1 = { 10, 20, 30, 40 };
int[] arr2 = { 10, 200, 30, 40, 50};
Arrays are not equal

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