Add Strings
Given two non-negative integers, num1 and num2, represented as strings, return the sum of num1 and num2 as a string.
You must solve the problem without using any built-in library for handling large integers such as BigInteger. You must also not convert the inputs to integers directly.
Example 1
Input
num1 = "11", num2 = "123"Output
"134"Adding 11 and 123 gives 134.
Example 2
Input
num1 = "456", num2 = "77"Output
"533"Adding 456 and 77 gives 533.
Constraints
- 1 <= num1.length, num2.length <= 10^4
- num1 and num2 consist of only digits.
- num1 and num2 don't have any leading zeros except for the zero itself.