Card Number and Application ID Parsing

CodingStripeLast reported October 2025Low Frequency

Reported: 3× across candidate reports
First seen: February 2025
Last reported: October 2025
Reported outcome: mixed

Problem Overview

You are given a card data string where the first two digits encode the length of the following field, which contains an Application ID (AID) or card number. Parse and validate the card information according to this length-prefixed encoding scheme. The problem is structured in multiple parts: Part 1 typically…

2 candidate-reported follow-ups — the exact probes interviewers asked, with the trigger for each
The rest of the problem statement — full requirements, constraints, and edge cases
Approach and trade-offs — what passing candidates did, and the mistakes that sink people

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Verified Source

Every question is reconstructed from multiple independent candidate reports. Verbatim follow-ups, not invented ones.

Codex Fact-Checked

Technical claims, formulas, and scale numbers are reviewed against primary sources.

Interviewer Follow-ups

The exact follow-ups reported by candidates, with the trigger that prompts each one — plus the mistakes that sink people.