How should I practice Account Balance Manager Part 2 - Reject Overdrafts?

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

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Problem · Hash Table

Account Balance Manager Part 2 - Reject Overdrafts

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This continues the account balance manager. You are given a list of transactions in order, each "account_id,amount" (positive = deposit, negative = withdrawal).

Now check the balance before applying each transaction. If a withdrawal would make the account's balance go negative, reject it: do not apply it and do not change the balance. Deposits are always allowed. A transaction that leaves the balance at exactly zero is allowed.

Return the list of rejected transactions, in the order they occurred, as a String[] with each entry formatted "account_id,amount".

Examples

01 · Example 1

transactions = ["account_A,100", "account_A,-150", "account_B,50", "account_A,-80", "account_B,-100"]
return = ["account_A,-150", "account_B,-100"]

Step 1: account_A +100 -> 100 (ok). Step 2: account_A -150 -> would be -50 (REJECT). Step 3: account_B +50 -> 50 (ok). Step 4: account_A -80 -> 100-80=20 (ok). Step 5: account_B -100 -> would be -50 (REJECT). The two rejected transactions are returned in order.

02 · Example 2

transactions = ["account_A,40", "account_A,-40", "account_A,-1"]
return = ["account_A,-1"]

account_A +40 -> 40 (ok). account_A -40 -> exactly 0, which is allowed (ok). account_A -1 -> would be -1 (REJECT). Only the last transaction is rejected.

Constraints

Each transaction is "account_id,amount" with an integer amount.
Process in order; reject a transaction whose application would make the balance strictly negative.
Deposits are always allowed; a result of exactly 0 is allowed.
A rejected transaction does not change any balance.
Return rejected transactions in order as "account_id,amount".