Implement Card Validation and Recovery System

Q: Implement Card Validation and Recovery System

This question evaluates algorithmic problem-solving and implementation skills in string processing, checksum validation (Luhn), pattern matching, combinatorics for counting masked completions, and single-error recovery for payment-card numbers.

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Design and implement a payment-card validation system supporting:

Basic VISA validation (16-digit numbers starting with 4) using the Luhn checksum.

Multi-network validation for VISA, MASTERCARD (16 digits, prefixes 51- 55) and AMEX (15 digits, prefixes 34 or 37), returning UNKNOWN_NETWORK or INVALID_CHECKSUM when appropriate.

Redacted cards containing 1-5 ‘*’ wildcards: count all valid completions per network and output counts sorted alphabetically by network.

Corrupted cards ending in ‘?’ with exactly one error (one digit changed or two adjacent digits swapped): enumerate all possible original valid card numbers with their network names, sorted numerically.

Follow all formatting and performance constraints described in the prompt.

Implement Card Validation and Recovery System

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