char[] aArray = a.ToCharArray();
            char[] bArray = b.ToCharArray();  
            Array.Sort(aArray);
            Array.Sort(bArray);  
            int i = 0, j = 0;
            int count = 0;
            while (i < aArray.Length && j < bArray.Length)
            {
                 if (aArray[i] == bArray[j])
                 {
                        i++;
                        j++;
                 }
                 else if (aArray[i] < bArray[j])
                 {
                        i++;
                        count++;
                 }
                else
             {
                     j++;
                     count++;
             }
        }
        if(i < aArray.Length)
        {
             count += aArray.Length - i;
        }
        if(j < bArray.Length)
        {
             count += bArray.Length - j;
        }

        return count;