Compute dasher pay from order events

Dasher naive pay (active-time with overlapping orders)

You are given a list of events describing when a delivery driver ("Dasher") accepts and fulfills different orders.

Pay rules

• Base rate: $0.30 per minute.
• An order is active from the time it is ACCEPTed until it is FULFILLed.
• Pay is multiplicative by concurrency: for each minute, the dasher earns

[ \text{pay per minute} = (#\text{active orders during that minute}) \times 0.30 ]

Input

events: a list of records (time, orderId, action) where:

• time is an integer timestamp in minutes (e.g., minutes since midnight).
• orderId is a string identifier.
• action is one of: ACCEPT, FULFILL.

Output

Return the total pay as a double, rounded to two decimals.

Important details / assumptions

• events may be unsorted; you must process them in increasing time.
• If multiple events have the same time, process all ACCEPT actions before FULFILL actions at that same time.
• Pay accrues over each interval between consecutive event timestamps. For an interval [t_i, t_{i+1}), the number of active orders is considered constant and equals the active set after applying all actions at t_i.
• You may assume the input is valid: each order is accepted before it is fulfilled.

Example

Events:

• 06:15 A ACCEPT
• 06:18 B ACCEPT
• 06:36 A FULFILL
• 06:45 B FULFILL

Pay:

• 06:15–06:18: 1 active × 3 min × 0.3 = 0.9
• 06:18–06:36: 2 active × 18 min × 0.3 = 10.8
• 06:36–06:45: 1 active × 9 min × 0.3 = 2.7

Total = 14.4