Write reverse_number(n) that returns the integer whose digits are those of n in reverse order. The sign stays where it is, and leading zeros disappear because the result is an integer.
Examples
Input: n = 1230
Output: 321
Input: n = -450
Output: -54
Input: n = 0
Output: 0
Constraints
-10**15 <= n <= 10**15
Goals
- Build a number digit by digit
- Preserve the sign and drop leading zeros