How should I practice Credit Card Command Processor?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Chime phone screen problems in FastPrep.

Is Credit Card Command Processor associated with Chime?

FastPrep tags this as a Chime phone screen coding practice problem when the problem catalog has that company and stage context.

Problem · Array

Credit Card Command Processor

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ChimeFULLTIMEPHONE SCREEN

Problem statement

Process a batch of credit-card commands. Each cardholder is added at most once and starts with balance $0.

Command	Behavior
`["Add", name, cardNumber, "$limit"]`	Create the account. A card is valid only when it has 12 to 16 digits and passes the Luhn check.
`["Charge", name, "$amount"]`	Increase a valid card's balance unless the new balance would exceed its limit. Ignore the command for an invalid card.
`["Credit", name, "$amount"]`	Decrease a valid card's balance. Negative balances are allowed. Ignore the command for an invalid card.

Return one row per cardholder, sorted by name. A valid card returns [name, "$balance"]; an invalid card returns [name, "error"].

Function

processCardCommands(operations: String[][]) → String[][]

Examples

Example 1

operations = [["Add","Tom","4111111111111111","$1000"],["Add","Lisa","5454545454545454","$3000"],["Add","Quincy","12345678901234","$2000"],["Charge","Tom","$500"],["Charge","Tom","$800"],["Charge","Lisa","$7"],["Credit","Lisa","$100"],["Credit","Quincy","$200"]]return = [["Lisa","$-93"],["Quincy","error"],["Tom","$500"]]

Tom's second charge is declined because it would exceed his limit. Lisa's credit makes her balance negative, and Quincy's invalid card reports an error.

Example 2

operations = [["Add","Amy","4012888888881881","$100"],["Add","Zed","123456789012","$50"],["Charge","Amy","$100"],["Charge","Amy","$1"],["Credit","Amy","$25"],["Credit","Zed","$10"]]return = [["Amy","$75"],["Zed","error"]]

Amy reaches her limit, the next charge is ignored, and a later credit lowers the balance. Zed's invalid card ignores its credit.

Constraints

1 <= operations.length <= 100000.
Every operation has one of the documented shapes, and every referenced name was added earlier.
Names contain between 1 and 50 ASCII letters and are unique.
Limits and amounts are decimal integers between 0 and 10^9 prefixed by $.
Every valid account balance fits in a signed 64-bit integer.