Thread: ArrayDiff Problem on CodeWars; Need Assistance

Sorry about that. New to this forum.

To be honest those questions about what is in the arguments isn't really the issue.
But I will try posting another question on Codewars and see if I can get some clarification.

I'm just wondering, how do I write code for this problem in Java?
I just need to return array a with all values present in array b removed.

Is it true all arrays in Java are immutable?
Can I add to an empty array that's dynamic (not a fixed size) in Java?

For example, would this code be a possible solution?

 
public class Kata {
 
  public static int[] arrayDiff(int[] a, int[] b) {
    HashSet<Integer> result = new HashSet<>();
    Arrays.sort(b);
    for (int elem : a) {
      if (Arrays.binarySearch(b, elem) < 0)
        result.add(elem);
    }
    int[] arr = new int[result.size()];
    int i = 0;
    for (int elem : result) {
      arr[i++] = elem;
    }
    return arr;
  }
 
}

Or could I use an ArrayList to append to instead? Would an ArrayList be better than a HashSet?
You need to import the java.util package to access ArrayLists right?

I've adjusted my code to use ArrayList instead of HashMap.
I've included comments to explain what is happening.

I've tried executing the code in the Java Tutor at Java Tutor - Visualize Java code execution to learn Java online
It produces an error once it reaches "result.add(elem);"

import java.util.ArrayList;
import java.util.Arrays;
public class Kata {
 
  public static int[] arrayDiff(int[] a, int[] b) {
// Initialize ArrayList to add elements from int[] a 
    ArrayList<String> result = new ArrayList<String>();
// sort int[] b in order to binarySearch it for any element present in int[] a
    Arrays.sort(b);
// If an element is present in a but is NOT present in b then add to result ArrayList
    for (int elem : a) {
      if (Arrays.binarySearch(b, elem) < 0)
        result.add(elem); // error occurs here
    }
// Initialize integer array to transfer elements from result ArrayList
    int[] arr = new int[result.size()];
    int i = 0;
    for (int elem : result) {
      arr[i++] = elem;
    }
    return arr;
  }
 
// I don't know how to execute the code in Java
// Is this how you call the function?
}
public static int[] main(int[] args) {
    arrayDiff({1, 2}, 2, {1}, 1, *z);
  }

I tried executing the code but it produces this message:

Error: no suitable method found for add(int)
method java.util.Collection.add(java.lang.String) is not applicable
(argument mismatch; int cannot be converted to java.lang.String)
method java.util.List.add(java.lang.String) is not applicable
(argument mismatch; int cannot be converted to java.lang.String)
method java.util.AbstractCollection.add(java.lang.String) is not applicable
(argument mismatch; int cannot be converted to java.lang.String)
method java.util.AbstractList.add(java.lang.String) is not applicable
(argument mismatch; int cannot be converted to java.lang.String)
method java.util.ArrayList.add(java.lang.String) is not applicable
(argument mismatch; int cannot be converted to java.lang.String)

--- Update ---

I solved it!
My solution works in CodeWars.
For some reason it wasn't executing in the Java Tutor

Here is the final solution I used:

import java.util.ArrayList;
import java.util.Arrays;
public class Kata {
 
  public static int[] arrayDiff(int[] a, int[] b) {
    ArrayList<Integer> result = new ArrayList<>();
    Arrays.sort(b);
    for (int elem : a) {
      if (Arrays.binarySearch(b, elem) < 0)
        result.add(elem);
    }
    int[] arr = new int[result.size()];
    int i = 0;
    for (int elem : result) {
      arr[i++] = elem;
    }
    return arr;
  }
}