public static List<Integer> icecreamParlor(int m, List<Integer> arr) {
    List<Integer> result = new ArrayList<>();
    for(int i=0;i<arr.size()-1;i++) {
        int diff = m-arr.get(i);
        int idx = arr.indexOf(diff);
        if(idx == i) {
            idx = arr.subList(i+1, arr.size()).indexOf(diff);
            if(idx != -1) idx = i+1+idx;
        }
        if(idx == -1) continue;

        result.add(i+1);
        result.add(idx+1);
        return result;
    }
    return result;
}