How should I practice Register and Transfer Brazilian Receivables?

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Register and Transfer Brazilian Receivables

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Problem statement

Brazilian card transactions are registered as daily receivables. You are given two CSV strings.

transactionsCsv has header customer_id,merchant_id,payout_date,card_type,amount.
contractsCsv has header contract_id,merchant_id,payout_date,card_type,amount. It may contain only the header.

First aggregate all transactions by (merchant_id, card_type, payout_date), summing their amounts. Then apply every contract. A contract replaces the matching merchant receivable: remove that merchant row and create a row identified by the contract ID with the contract's card type, payout date, and amount.

Return CSV rows beginning with id,card_type,payout_date,amount. Sort the data rows by Unicode code points in ID, then card type, then payout date. When all three strings are equal, sort by amount numerically in ascending order. Write each output amount in base-10 notation without leading zeros.

Function

registerReceivables(transactionsCsv: String, contractsCsv: String) → String[]

Examples

Example 1

transactionsCsv = "customer_id,merchant_id,payout_date,card_type,amount\ncust1,merchantA,2021-12-30,Visa,150\ncust2,merchantA,2021-12-30,Visa,200\ncust3,merchantB,2021-12-31,MasterCard,300\ncust4,merchantA,2021-12-30,Visa,50"contractsCsv = "contract_id,merchant_id,payout_date,card_type,amount"return = ["id,card_type,payout_date,amount","merchantA,Visa,2021-12-30,400","merchantB,MasterCard,2021-12-31,300"]

The three matching merchant-A Visa transactions aggregate to 400. No contract replaces either receivable.

Example 2

transactionsCsv = "customer_id,merchant_id,payout_date,card_type,amount\ncust1,merchantA,2022-01-05,Visa,300\ncust2,merchantA,2022-01-05,Visa,200\ncust3,merchantB,2022-01-06,MasterCard,1000"contractsCsv = "contract_id,merchant_id,payout_date,card_type,amount\ncontract1,merchantA,2022-01-05,Visa,500"return = ["id,card_type,payout_date,amount","contract1,Visa,2022-01-05,500","merchantB,MasterCard,2022-01-06,1000"]

The contract replaces merchant A's matching receivable. Merchant B's receivable remains.

Example 3

transactionsCsv = "customer_id,merchant_id,payout_date,card_type,amount\ncust1,merchantA,2022-01-07,Visa,500\ncust2,merchantA,2022-01-07,Visa,250\ncust3,merchantB,2022-01-08,MasterCard,1250\ncust4,merchantC,2022-01-09,Visa,1500"contractsCsv = "contract_id,merchant_id,payout_date,card_type,amount\ncontract1,merchantA,2022-01-07,Visa,750\ncontract2,merchantC,2022-01-09,Visa,1500"return = ["id,card_type,payout_date,amount","contract1,Visa,2022-01-07,750","contract2,Visa,2022-01-09,1500","merchantB,MasterCard,2022-01-08,1250"]

Two merchant receivables are replaced by contracts. The remaining rows are returned in the required deterministic order.

Constraints

Each CSV contains a valid fixed header and between 0 and 100000 data rows.
Fields contain no commas, line breaks, or surrounding whitespace.
IDs, card types, and payout dates are non-empty.
Amounts are positive integers at most 10^9; every aggregate fits a signed 64-bit integer.
Each contract maps to exactly one aggregated merchant receivable, and no two contracts map to the same receivable.