Count completed car journeys from sensor logs

You are given a time-ordered list of highway sensor logs. Each log entry contains:

• timestamp (integer; strictly increasing)
• sensor_type (one of "ENTRY", "EXIT", "CHECKPOINT")
• car_id (string)

A journey is defined as: for the same car_id, an ENTRY event followed later by an EXIT event. CHECKPOINT events may occur in between but do not affect the definition.

A car may make multiple journeys over time (e.g., ENTRY ... EXIT ... ENTRY ... EXIT). If a car has an ENTRY without a subsequent EXIT by the end of the logs, that partial journey does not count. If an EXIT occurs when the car is not currently in an active journey (i.e., there was no unmatched prior ENTRY), ignore it.

Write a function that returns the total number of completed journeys across all cars.

Example:

Logs:

1. (1, "ENTRY", "A")
2. (2, "CHECKPOINT", "A")
3. (3, "EXIT", "A")
4. (4, "EXIT", "B")
5. (5, "ENTRY", "A")
6. (6, "ENTRY", "B")
7. (7, "EXIT", "B")

Result: 2 (A completes 1 journey at t=3; B completes 1 journey at t=7).

Count Completed Car Journeys from Sensor Logs

You are given a time-ordered list of highway sensor logs. Each log entry is a tuple of the form (timestamp, sensor_type, car_id), where sensor_type is one of "ENTRY", "EXIT", or "CHECKPOINT".

A completed journey happens when the same car_id has an "ENTRY" event followed later by an "EXIT" event. "CHECKPOINT" events may appear in between and do not affect the journey state.

Rules:

• An "ENTRY" starts a journey for that car if it is not already in an active journey.
• An "EXIT" completes a journey only if the car currently has an unmatched prior "ENTRY".
• If an "EXIT" appears for a car with no active journey, ignore it.
• If a car is already in an active journey and another "ENTRY" appears before an "EXIT", ignore the extra "ENTRY".
• Any car still in an active journey at the end of the logs does not count as completed.

Return the total number of completed journeys across all cars.

Constraints

• 0 <= len(logs) <= 200000
• Each log entry is (timestamp, sensor_type, car_id), with strictly increasing integer timestamps
• sensor_type is one of "ENTRY", "EXIT", or "CHECKPOINT"

Hints

1. Think about what information you need to remember for each car while scanning the logs from left to right.
2. Because the logs are already time-ordered, a single pass with a hash set is enough.