Detecting duplicates in an array

Question

Pretty new to this and I've exhausted numerous attempts to figure out why this isn't working but can't get it.

private int indexOf(int searchingNum)
{
    int x = searchingNum;
    for (int i = 0; i<numberArray.length; i++){
        if (numberArray[i]==x)
            index = i;
        else
            index = -1;
    }
    return index;
}

public boolean addNumber(int numberToAdd)
{
    int x = numberToAdd;
    if (indexOf(x)!=-1)
        return false;
    if (count<numberArray.length&&indexOf(x)==-1){
        count++;
        numberArray[count-1] = x;
        return true;
    }

    if  (count>=numberArray.length&&indexOf(x)==-1){
        count++;
        newArray = Arrays.copyOf(numberArray, 2* numberArray.length);
        numberArray = newArray;
        numberArray[count-1] = x;
    }
    return true;    
}

The method should't allow for duplicates but does. Any pointers in the right direction would be much appreciated.

Thank you.

If you want to avoid duplicates, consider using a Set instead of an array. — Frank Puffer
– Frank Puffer, Commented Feb 18, 2017 at 20:32

Sergey Kalinichenko · Accepted Answer · 2017-02-18 20:29:00Z

2

Your indexOf is incorrect: since you continue the loop after finding a match, your code returns -1 unless the last item in the array happens to match.

To fix this problem, return i from inside the loop:

for (int i = 0 ; i < numberArray.length ; i++) {
    if (numberArray[i]==x)
        return i;
}
// If we are here, we did not find anything; return -1
return -1;

answered Feb 18, 2017 at 20:29

Sergey Kalinichenko

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1 Comment

Jordan Cook Over a year ago

I can't believe I didn't see that! Thank you! Problem resolved.

Subhranil · Accepted Answer · 2017-02-18 20:41:33Z

Here's a precise version of your code :

private boolean contains(int searchingNum)
{
    for (int i = 0; i<numberArray.length; i++){
        if (numberArray[i]==x)
            return true;
    }
    return false;
}

public boolean addNumber(int numberToAdd)
{
    int x = numberToAdd;
    if (contains(x))
        return false;
    if (count<numberArray.length){
        count++;
        numberArray[count-1] = x;
}
   else{
        count++;
        int []newArray = Arrays.copyOf(numberArray, 2* numberArray.length);
        numberArray = newArray;
        numberArray[count-1] = x;
    }
    return true;    
}

Try this. Meanwhile, it can only gurantee you the uniqueness of the elements if the array wasn't previously initialised, i.e. all elements are added in the array using this method only.

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