How would you add two very large numbers? (approach only)
Asked in the Round 1 stage. Implement string-based addition without converting either input to a built-in numeric type.
Given two canonical decimal strings num1 and num2, return their exact sum as a decimal string.
Example 1: num1 = "12345678901234567890", num2 = "9876543210" returns "12345678911111111100".
Example 2: num1 = "999", num2 = "1" returns "1000", because the carry propagates across every digit.
def add_large_numbers(num1, num2):