Passenger Boarding Count Per Bus

A transit analytics team needs a deterministic boarding ledger: for every scheduled bus, report exactly how many passengers board it under first-eligible pickup rules.

Table: Buses

• bus_id: unique identifier for a bus trip
• arrival_time: time when that bus arrives at the station

Table: Passengers

• passenger_id: unique passenger identifier
• arrival_time: time when the passenger reaches the station

Boarding policy:

• A passenger boards the earliest bus whose arrival_time is greater than or equal to the passenger arrival_time.
• A passenger can board at most one bus.
• If all buses arrive earlier than a passenger, that passenger is not boarded.

Task: For each bus in Buses, return how many passengers board that bus.

Output requirements:

• Return exactly two columns:
  1. bus_id
  2. passengers_cnt
• Return one row for every bus.
• Sort by bus_id in ascending order.

Supported submission environments:

• SQL (SQLite 3.27.2)
• Pandas (Python)