Query Order and Batch Lifetimes from Event Files

Problem Statement

In trading systems, orders are often submitted individually or grouped into logical execution batches. You are given a stream of chronological order lifecycle events from an event log. Each event records a timestamp, an action ("CREATE" or "CLOSE"), an order_id, and an optional batch_id (present on "CREATE").

Implement the OrderLifetimeTracker class with the following methods:

• process_event(timestamp: int, action: str, order_id: str, batch_id: str | None = None) -> None: Ingests an event. Actions are either "CREATE" (which opens the order at timestamp and associates it with batch_id if provided) or "CLOSE" (which marks the order as finished at timestamp).
• get_lifetime(identifier: str) -> tuple[int, int] | None: Queries the lifetime (start_time, end_time) for a given identifier:
  • If identifier is an order_id:
    • start_time is the timestamp when the order was created.
    • end_time is the timestamp when the order closed, or 0 if it is still open.
  • If identifier is a batch_id:
    • start_time is the earliest creation timestamp among all orders in the batch.
    • end_time is the latest close timestamp among all orders in the batch. However, if any order in the batch is still open, end_time must be 0.
  • If identifier matches neither an existing order nor a batch, return None.

You may assume all order_id and batch_id values come from disjoint sets (no ID is used as both an order and a batch).

Interface

class OrderLifetimeTracker:
    def __init__(self):
        pass

    def process_event(self, timestamp: int, action: str, order_id: str, batch_id: str | None = None) -> None:
        pass

    def get_lifetime(self, identifier: str) -> tuple[int, int] | None:
        pass

Constraints

• Timestamps are positive integers strictly increasing or non-decreasing: 1 <= timestamp <= 10^9.
• Each order_id is created at most once and closed at most once.
• An order is never closed before it is created.
• Total number of events and queries N <= 200,000.
• get_lifetime should execute in O(1) time.

Example

tracker = OrderLifetimeTracker()

# Order 1 and Order 2 belong to Batch B1
tracker.process_event(100, "CREATE", "O1", "B1")
tracker.process_event(105, "CREATE", "O2", "B1")

# Order 3 is standalone (no batch)
tracker.process_event(110, "CREATE", "O3", None)

# Close O1
tracker.process_event(150, "CLOSE", "O1")

tracker.get_lifetime("O1")  # returns (100, 150)
tracker.get_lifetime("O2")  # returns (105, 0) -> still open
tracker.get_lifetime("B1")  # returns (100, 0) -> O2 is still open, so end is 0
tracker.get_lifetime("O3")  # returns (110, 0)

# Close O2
tracker.process_event(180, "CLOSE", "O2")
tracker.get_lifetime("B1")  # returns (100, 180) -> all orders closed
tracker.get_lifetime("UNKNOWN")  # returns None