Adding integers to an array with a for loop

Question

I have a problem with removig duplicate elements from an array in Java. I made two extra functions, one which counts how many unique elements there are and one which checks if the integer is already in the result array. Everything seems to work, but I fail a test where 0 is supposed to be 2nd in the array, but it's always moved to the end in my code. What can I do to fix this mistake?

Tester is showing this error:

Expected :is [<100>, <0>, <3>, <4>, <562>]

Actual :[<100>, <3>, <4>, <562>, <0>]

This is my code so far:

public static int[] removeDuplicates(int[] integers) {
    int count = countUniques(integers);
    int counter = 0;
    int[] result = new int[count];
    for (int integer : integers) {
        Boolean isInArray = isInArray(result, integer);
        if (!isInArray) {
            result[counter] = integer;
            counter++;
        }
    }
    return result;
}


public static int countUniques(int[] integers) {
    int i, j;
    int count = 0;
    for (i = 0; i < integers.length; ++i) {
        for (j = 0; j < i; j++)
            if (integers[i] == integers[j])
                break;
        if (i == j)
            count++;
    }
    return count;
}

public static Boolean isInArray(int[] integers, int targetInteger) {
    for (int integer : integers) {
        if (targetInteger == integer) {
            return true;
        }
    }
    return false;
}

int[] result = new int[count]; - the result array is by default filled with 0s, so isInArray(result, 0); will always return true. You need to approach this problem in a different way (an ArrayList would be an option. Or manually resizing the array whenever you add a new element) — UnholySheep
– UnholySheep, Commented Feb 14, 2022 at 19:29

user1738539 · Accepted Answer · 2022-02-14 19:43:24Z

1

When you create a primitive int array it is by default filled with 0s. You can change your code to use an Integer object array. That way the default value for each element will be null.

You would then need to null check each element inside your isInArray():


public static Boolean isInArray(Integer[] integers, int targetInteger) {
    for (Integer integer : integers) {
        if (integer != null && targetInteger == integer) {
            return true;
        }
    }
    return false;
}

And change your result array to Integer[] result = new Integer[count]; and return Integer[] instead of int[].

If you want to return primitive array you can use streams and map Integer to int.

something like return Arrays.stream(result).mapToInt(i-> i).toArray();

answered Feb 14, 2022 at 19:43

user1738539

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Comments

Chris Foley · Accepted Answer · 2022-02-14 19:53:47Z

You haven't filled up the result array yet, so the end of it will be filled with zeros. You only want to loop over the part that you have filled. One way to achieve this is to pass the value of counter to your isInArray method.

public static int[] removeDuplicates(int[] integers) {
    int count = countUniques(integers);
    int counter = 0;
    int[] result = new int[count];
    for (int integer : integers) {
        Boolean isInArray = isInArray(result, counter, integer);
        if (!isInArray) {
            result[counter] = integer;
            counter++;
        }
    }
    return result;
}


public static int countUniques(int[] integers) {
    int i, j;
    int count = 0;
    for (i = 0; i < integers.length; ++i) {
        for (j = 0; j < i; j++)
            if (integers[i] == integers[j])
                break;
        if (i == j)
            count++;
    }
    return count;
}

public static Boolean isInArray(int[] integers, int integersLength, int targetInteger) {
    for (int i = 0; i < integersLength; i++) {
        if (targetInteger == integers[i]) {
            return true;
        }
    }
    return false;
}

hfontanez · Accepted Answer · 2022-02-14 20:32:17Z

If you need to remove duplicates from an array, probably the simplest thing to do is to convert the array to a java.util.Set and then convert the set back to an array.

public int[] removeDups(int[] arr) {
    Set<Integer> noDups = new HashSet<>(Arrays.stream(arr).boxed().collect(Collectors.toList()));
    int[] newArr = noDups.stream().mapToInt(Integer::intValue).toArray();
    return newArr;
}

This simplifies the process and eliminates additional issues like the one you are having with creating an array padded with zeros for the unused array index locations.

To count "unique", call this method and then return the created collection's size:

public int countUnique(int[] arr) {
    return removeDups(arr).length;
}

This solution does not require the method isInArray; which by the way, should not be a public method. In my opinion, public methods should not invoke other public methods. The reason being is that requirement's change might cause the method with the dependency to break.

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