public static List<Integer> icecreamParlor(int m, List<Integer> arr) {
    int n = arr.size();
    Integer[] indices = new Integer[n];
    
    for (int i = 0; i < n; i++) {
        indices[i] = i;
    }
    
    Arrays.sort(indices, Comparator.comparingInt(i -> arr.get(i)));
    Collections.sort(arr);
    
    int i = 0, j = n - 1;
    while(i <= j){
      if( arr.get(i) + arr.get(j)  > m)
        j--;
      else if(arr.get(i) + arr.get(j)  < m)
        i++;
      else{
        int firstIndex = indices[i] + 1;
        int secondIndex = indices[j] + 1;
        List<Integer>result = Arrays.asList(firstIndex, secondIndex);
        Collections.sort(result);
        return result;
        }  
      }
    return new ArrayList();
    }