The core logic isn't too bad once you think of it like grade school subtraction, right-align, borrow, repeat.
Clarify that the problem is essentially string-based subtraction, similar to manual subtraction but with possible negative results. Compare the two numbers by length and lexicographic order to determine the sign, then perform subtraction digit by digit from right to left, handling borrows. Finally, strip leading zeros and prepend a minus sign if needed.
Pro tip: Mention that you would first normalize the inputs by stripping leading zeros to simplify comparisons, and use a helper function to subtract the smaller absolute value from the larger to avoid code duplication. Also, discuss edge cases like equal numbers and zero results early to show thoroughness.
Confirm that inputs are non-negative strings and may have leading zeros. Strip leading zeros from both strings to simplify comparison and subtraction.
Compare the normalized strings by length and lexicographic order to decide which number is larger. This determines the sign of the result and which number to subtract from which.
Iterate from the least significant digit to the most significant, subtracting the smaller number from the larger. Maintain a borrow variable and compute each digit as (digitA - borrow - digitB + 10) % 10, updating borrow accordingly.
Build the result string by appending digits in reverse order, then strip any leading zeros. If the result is empty, return '0'. If the original larger number was the second input, prepend a minus sign.
Verify with cases like equal numbers (result '0'), one number zero, negative results, and inputs with many leading zeros. Ensure no leading zeros in the output except for '0' itself.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.