Validate Credit Card Numbers and Corrections

Q: Validate Credit Card Numbers and Corrections

This question evaluates understanding and implementation of checksum algorithms (Luhn), pattern matching for card-brand identification, string processing with wildcards, combinatorial counting, and error-correction enumeration in the Coding & Algorithms category.

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Q1. Given a credit-card number string, return whether it passes the Luhn checksum and, if valid, identify its brand among VISA (16 digits starting with 4), MASTERCARD (16 digits starting with 51– 55) or AMEX (15 digits starting with 34 or 37); otherwise output "INVALID_CHECKSUM". Q2. Extend Q1 so that a number passing the Luhn check but matching none of the three known patterns is labeled "UNKNOWN". Q3. Given a partially redacted card string containing '*' wildcards (each stands for any single digit), output the count of possible valid card numbers for every brand it could represent (e.g., "VISA,1"). Wildcards may cause overlaps where the same pattern fits multiple brands. Q4. Given an observed card string ending with '?' indicating exactly one corruption (single‐digit change, deletion, insertion, or adjacent swap) in the preceding digits, enumerate every original card number that would have been valid before the error.

Validate Credit Card Numbers and Corrections

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