Minimum Sum of Four-Digit Number After Splitting Digits

class Solution {
    public int minimumSum(int num) {
        List<Integer> list = new ArrayList<>();
        while(num != 0){
            int n = num%10;
            if(n != 0)
                list.add(n);
            num /= 10;
        }
        Collections.sort(list, Collections.reverseOrder());
        if(list.size() == 1)
            return list.get(0);
        else if(list.size() == 2)
            return list.get(0) + list.get(1);
        else if(list.size() == 3)
            return (list.get(0) + 10 * list.get(2)) + list.get(1);
        else
            return (list.get(0) + 10 * list.get(2)) + (list.get(1) + 10 * list.get(3));
    }
}