Question

I’m trying to write a method that takes 2 ArrayLists of doubles and returns all the values in set1 that aren’t found in set2. These numbers should be returned in set3. I keep getting an out of memory error. Can anyone point me in the right direction?

ArrayList<Double> setDiff(ArrayList<Double> set1, ArrayList<Double> set2){
    ArrayList<Double> set3 = new ArrayList<Double>();
    int count = 0;
    while(count < set1.size()){
        boolean inList = false;
        while(inList == false){
            int count2 = 0;
            while(count2 < set2.size() && set1.get(count) == set2.get(count2)){
                count2++;
            }
            if(count2 != set2.size()){
                set3.add(set1.get(count));
            }
            else{
                inList = true;
                count++;
            }
        }
    }

    return set3;
}

Answer 1

Some loop is likely not stopping as you would expect.

The following code snippet would accomplish pretty much the same you are trying to do.

for (Double d : set1) {
    if (!set2.contains(d)) {
        set3.add(d);
    }
}

UPDATE: since you say you cannot use contains(), you can perform the checks by yourself:

for (Double d : set1) {
        boolean found = false;
        for (int i=0; i<set2.size() && !found; i++) {
                if (d.equals(set2.get(i))) {
                    found = true;
            }
        }
        if (!found) {
            set3.add(d);
        }
}

EDIT: Furthermore, the problem in your code lies in the line

  if(count2 != set2.size()){

You should change != with >, since in the case of being count2 less than set2, the external count variable will not increase, resulting in an infinite loop, and after a few seconds, an OutOfMemoryError.

Also, your algorithm wasn’t 100% correct either, since the looping through the second list was not consistent. You can see a similar approach with while-loops below:

                int count = 0;
                while (count < set1.size()) {
                    boolean inList = false;
                    int count2 = 0;
                    while (inList == false && count2 < set2.size()) {
                        if (set1.get(count).equals(set2.get(count2))) {
                            inList = true;
                        }
                        count2++;
                    }
                    if (!inList) {
                            set3.add(set1.get(count));
                    }
                    count++;
               }