How should I practice Account Balance Manager Part 3 - Platform Coverage?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Stripe onsite interview problems in FastPrep.

Is Account Balance Manager Part 3 - Platform Coverage associated with Stripe?

FastPrep tags this as a Stripe onsite interview coding practice problem when the problem catalog has that company and stage context.

Problem · Hash Table

Account Balance Manager Part 3 - Platform Coverage

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Problem statement

Source note: July 26, 2026 — 🌺 I re-audited the original author-written sources and rebuilt this practice version from the available interview reports. It is about a 25% match to the available source. The Stripe coding-round context, Account Balance / Bank Transaction topic, three-question progression, and platform-account coverage idea come directly from the sources. The source says a platform account is passed in and its money can cover other negative accounts, but it does not show allocation order, exact return value, failure behavior, signature, examples, constraints, or edge cases. FastPrep supplied those details as a bounded runnable contract without claiming they were present in the report. If a more complete author-written source becomes available, I will continue refining this problem step by step.

Practice sequence

Part 1: Calculate Totals
Part 2: Reject Overdrafts
Part 3: Platform Coverage (you are here)

What the interview report shared

The coding round centered on Account Balance / Bank Transaction and contained three questions.

Practice contract

For this exercise, assume transactions arrive in order as account_id,amount strings, every account starts with a balance of 0, and one identifier names the platform account.

Apply a transaction normally when the resulting balance is non-negative.
When a non-platform account would become negative, the platform covers exactly the shortfall so that account ends at 0.
The platform account's own transactions are never covered, and sufficient platform funding is available.

Return the total amount covered by the platform.

Function

processWithCoverage(transactions: String[], platformAccount: String) → int

Examples

Example 1

transactions = ["platform,1000", "account_A,100", "account_A,-150", "account_B,50", "account_B,-100", "account_A,-30"]platformAccount = "platform"return = 130

platform +1000 -> 1000. account_A +100 -> 100. account_A -150 -> would be -50, platform pays 50, account_A becomes 0 (covered total 50). account_B +50 -> 50. account_B -100 -> would be -50, platform pays 50, account_B becomes 0 (covered total 100). account_A -30 -> would be -30, platform pays 30, account_A becomes 0 (covered total 130). Total covered = 130.

Example 2

transactions = ["platform,500", "account_A,20", "account_A,-20"]platformAccount = "platform"return = 0

account_A +20 -> 20, then -20 -> exactly 0, which does not go negative, so no coverage is needed. The platform pays nothing.

Constraints

Each transaction is "account_id,amount" with an integer amount.
When a non-platform account would go negative, the platform covers the shortfall so that account ends at exactly 0, and the platform account is debited by that shortfall.
The platform account is treated as a normal account for its own transactions and is never itself covered.
Assume the platform always has enough money.
Return the total amount paid by the platform as an integer.