public static long ReverseNumber(this long number)
        {
            long reversedNumber = 0;
            bool isNegative = false;
 
            if (number < 0)
            {
                isNegative = true;
            }
            if (number < 10 && number >= 0)
            {
                reversedNumber = number;
                return reversedNumber;
            }
 
            number = Math.Abs(number);
 
            while (number > 0)
            {
                reversedNumber = _base * reversedNumber + number % _base;
                number = number / _base;
            }
 
            if (isNegative)
            {
                reversedNumber = reversedNumber * -1;
            }
            return reversedNumber;
        }

 

Test Case

Number 1234567890 is reversed to 987654321

Number -123456 is reversed to -654321

Number 9 is reversed to 9

Number 545 is reversed to 545

Number 123454321 is reversed to 123454321

Number -123454321 is reversed to -123454321