Find different index in arrays compare

July 18, 2022

I’m trying to learn a bit Java with tutorials and currently I’m struggling with piece of code where I should find on which index is difference between arrays (if there is difference at all)

My code

Scanner scanner = new Scanner(System.in);

int[] arrOne = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
int[] arrTwo = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
int sumArrOne = 0;
int index = 0;
boolean diff = false;

for (int k : arrOne) {
   if (Arrays.equals(arrOne, arrTwo)) {
       sumArrOne += k;
   } else {
       for (int i : arrTwo) {
           if (k != i) {
              index = i;
              diff = true;
               break;
           }
       }
   }
}
if (diff) {
    System.out.println("Found difference at " + index + " index.");
} else {
    System.out.println("Sum: " + sumArrOne);
}

So, if arrays are identical I’m sum array elements in arrOne. If they are not identical -> must show at which index they are not.

With this code when I input

1 2 3 4 5
1 2 4 3 5

I should get that difference is at index 2 instead I’ve got index 1.

I’m not quite sure why and would be glad if someone point me out where is my mistake.

>Solution :

I updated your code. Looks like you’re misunderstanding the concept of indexes yet.

Use one common index to check with in both arrays, in my example it’s simply called i:

import java.util.Arrays;
import java.util.Scanner;

public class BadArray {

    static private final int INVALID_INDEX = Integer.MIN_VALUE;

    public static void main(final String[] args) {
        try (final Scanner scanner = new Scanner(System.in);) {


            final int[] arrOne = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
            final int[] arrTwo = Arrays.stream(scanner.nextLine().split(" ")).mapToInt(Integer::parseInt).toArray();
            int sumArrOne = 0;
            int diffIndex = INVALID_INDEX;

            final int minLen = Math.min(arrOne.length, arrTwo.length);
            for (int i = 0; i < minLen; i++) {
                sumArrOne += arrOne[i];
                if (arrOne[i] != arrTwo[i]) {
                    diffIndex = i;
                    break;
                }
            }

            if (diffIndex != INVALID_INDEX) {
                System.out.println("Found difference at " + diffIndex + " index.");
            } else if (arrOne.length != arrTwo.length) {
                System.out.println("Arrays are equal but have different length!");
            } else {
                System.out.println("Sum: " + sumArrOne);
            }
        }
    }

}

I also put the scanner into a try-resource-catch to handle resource releasing properly.

Note you could also do the array lengths comparison right at the start if different array lengths play a more crucial role.