77. implement BigInt subtraction with sign
easy - accepted / - tried
This is a follow-up on 75. implement BigInt subtraction.
You are asked to implement a string substraction function, with possible negative integers. Also, '+' plus sign should also be supported
substract('-999999999999999999', '-1') // '-999999999999999998' substract('-999999999999999999', '+1') // '-1000000000000000000'
Don't use BigInt directly, it is not our goal here.