{"blocks": [{"key": "823fc545", "text": "Question", "type": "header-two", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, {"key": "a6345841", "text": "Design and implement a payment-card validation system supporting:", "type": "unstyled", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, {"key": "4e166a90", "text": "Basic VISA validation (16-digit numbers starting with 4) using the Luhn checksum.", "type": "unordered-list-item", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, {"key": "633dc95e", "text": "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.", "type": "unordered-list-item", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, {"key": "ef1fcc02", "text": "Redacted cards containing 1-5 ‘*’ wildcards: count all valid completions per network and output counts sorted alphabetically by network.", "type": "unordered-list-item", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, {"key": "e4b18bf5", "text": "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.", "type": "unordered-list-item", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, {"key": "02c61ce9", "text": "Follow all formatting and performance constraints described in the prompt.", "type": "unstyled", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}], "entityMap": {}}