DIY: Multiply Strings

Problem statement

You are given two non-negative integers represented as strings. Your task is to find the product of the given two integer numbers in the form of a string. For this, you will first convert the given strings to an integer without using the built-in library and then use the multiplication operator.

Constraints

• 1 <= firstNumber.length, secondNumber.length <= 200
• firstNumber and secondNumber consist of digits only.
• The firstNumber and the secondNumber do not contain any leading zero, except the number 0 itself.

Input

The inputs to the function are strings with integer values. The following is an example input:

firstNumber = 5
secondNumber = 6

Output

The following is the output of the above input:

30

Coding exercise

Implement the function multiply(firstNumber, secondNumber), which accepts two string arguments firstNumber and secondNumber storing non-negative integer numbers and returns the product of the two integers as a string.