Stripe 面试真题解析（四）：Brazil Receivables & Contracts（应收账款登记与合约更新）

Part 1: Register Receivables

Stripe in Brazil is obliged to register customer’s transactions for each merchant with the central bank as an aggregated unit per day. These are called receivables.
A receivable is identified by 3 identifiers:

• merchant_id (String): The id of the merchant on Stripe side.
• card_type (String): The type of the card used for the transaction (e.g. Visa).
• payout_date (String): String date of the funds available to the merchant by Stripe.

A payment transaction in Stripe API can be represented as the following object:

Transaction {
    string customer_id
    string merchant_id
    string payout_date
    string card_type
    int amount
}

Implement register_receivables function that takes a string in CSV format where each line represents a transaction and returns the registered aggregated receivables using the rules above.

Example input 1:

customer_id,merchant_id,payout_date,card_type,amount
cust1,merchantA,2021-12-30,Visa,150
cust2,merchantA,2021-12-30,Visa,200
cust3,merchantB,2021-12-31,MasterCard,300
cust4,merchantA,2021-12-30,Visa,50

Output 1:

id,card_type,payout_date,amount
merchantA,Visa,2021-12-30,400
merchantB,MasterCard,2021-12-31,300

Example input 2:

customer_id,merchant_id,payout_date,card_type,amount
cust1,merchantA,2021-12-29,MasterCard,50
cust2,merchantA,2021-12-29,Visa,150
cust3,merchantB,2021-12-31,Visa,300
cust4,merchantB,2021-12-29,MasterCard,200

Output 2:

id,card_type,payout_date,amount
merchantA,MasterCard,2021-12-29,50
merchantA,Visa,2021-12-29,150
merchantB,Visa,2021-12-31,300
merchantB,MasterCard,2021-12-29,200

Part 2: Contracts and Updates

In Brazil, settlement times can take up to 30 days for domestic card transactions.
Merchants can sell their receivables to a financial institution in order to get funds earlier.

Stripe is obliged to respect those contracts and update the registered receivables.
Each contract is mapped to one receivable using the same 3 identifiers as before:

• merchant_id
• card_type
• payout_date

In addition, merchants can sell part of their receivables and/or receive multiple contracts for the same receivable.

Safe assumptions:

• Contract amount will not exceed the receivable amount.
• If a receivable is sold fully, it should be returned as part of registered receivables with amount 0.
• Contracts will not have zero amounts.

Update the registered_receivables function implemented in Part 1 to reflect these new rules.

题目背景：

• 在巴西，Stripe 需要向央行登记每天的交易汇总信息（称为 receivables）。
• 每个 receivable 由商户 ID、卡类型和结算日期唯一标识。
• 输入是多条交易记录（CSV 格式），需要按规则聚合输出每日应收账款。
• 第二部分题目进一步引入 contracts（合同） 概念，要求更新 receivable 状态以反映部分或全部出售的情况。

考察点：

• 数据聚合与分组（group by 多键）；
• CSV 解析与输出；
• 状态更新逻辑（部分出售、全额出售）；
• 面向真实金融合规业务场景的建模与思维能力。

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