Your question is Add Large Integers as Strings. Start with the requirements on the right.
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Alteryx data workflows may receive numeric values whose length exceeds the limits of built-in integer types. Given two non-negative decimal integers as strings, return their exact sum as a decimal string without converting either input to an integer or using arbitrary-precision numeric libraries.
Implement add_strings(a, b), where a and b are non-empty strings containing only decimal digits. Inputs may contain leading zeros. Return a string containing the canonical decimal representation of a + b, with no leading zeros unless the result is "0".
The algorithm must work for inputs much larger than native numeric types. Do not use int, float, decimal, eval, or equivalent whole-string numeric conversion. Process digits from right to left, maintaining a carry, and ensure the running time is linear in the total input length.
def add_strings(a, b):