[Coding Quiz] Remove certain elements (or duplicate elements) in an arrary or string

        public static void RemoveZero(int[] arr)
        {
            int index = 0;
            for (int j = 0; j < arr.Length; j++)
            {
                if (arr[j] == 0) continue;
                else
                {
                    arr[index] = arr[j];
                    index++;
                }
            }

            for (int i = index; i < arr.Length; i++)
                arr[i] = 0;

        }

        public static void RemoveExtraSpace(char[] arr)
        {
            int index = 0;
            bool flag = false;      // ???
            for (int j = 0; j < arr.Length; j++)
            {
                if (arr[j] == ' ')
                {
                    if (!flag)
                    {
                        arr[index++] = arr[j];
                        flag = true;
                    }
                    else
                        continue;
                }
                else
                {
                    flag = false;
                    arr[index] = arr[j];
                    index++;
                }
            }

            for (int i = index; i < arr.Length; i++)
                arr[i] = ' ';

        }