How should I practice Driver Balance Ledger?

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

Is Driver Balance Ledger associated with Rippling?

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

Driver Balance Ledger

Rippling● EasyFULLTIMEPHONE SCREEN

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Problem statement

Maintain an in-memory balance ledger for delivery drivers. Process each operation in order:

["ADJUST", driverId, delta]: add the signed integer delta to the driver's current balance. A driver has balance 0 before the first adjustment.
["BALANCE", driverId]: append the driver's current balance to the result. An unseen driver has balance 0.
["TOTAL"]: append the sum of every driver's current balance to the result.

Only BALANCE and TOTAL operations produce output. Return those values in operation order.

The total-balance operation may be called very frequently, so it should not scan every driver on each call.

Function

processDriverBalances(operations: String[][]) → long[]

Examples

Example 1

operations = [["ADJUST","alice","1200"],["ADJUST","bob","800"],["TOTAL"],["BALANCE","alice"],["ADJUST","alice","-300"],["TOTAL"]]return = [2000,1200,1700]

After the first two adjustments, the total is 1200 + 800 = 2000. Alice's balance is 1200. Her final adjustment lowers both her balance and the cached total by 300, so the last result is 1700.

Example 2

operations = [["BALANCE","d7"],["TOTAL"],["ADJUST","d7","-50"],["BALANCE","d7"],["TOTAL"]]return = [0,0,-50,-50]

An unseen driver starts at 0, and an empty ledger also totals 0. Signed adjustments may make a balance and the overall total negative.

Example 3

operations = [["ADJUST","a","5"],["ADJUST","a","-5"],["ADJUST","b","9"],["TOTAL"],["BALANCE","a"],["BALANCE","b"]]return = [9,0,9]

Repeated adjustments accumulate for the same driver. Driver a returns to 0, while driver b contributes the entire total of 9.

Constraints

1 <= operations.length <= 2 * 10^5.
Each operation has one of the documented forms.
Each driverId contains 1 to 40 ASCII letters, digits, hyphens, or underscores.
Each delta is a decimal integer string between -10^9 and 10^9, inclusive.
Every individual driver balance and the total balance fit in a signed 64-bit integer.