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Count Complete Highway Journeys from Toll Logs

Quick Overview

Count completed highway journeys from unsorted entry, main-road, and exit toll records grouped by vehicle and direction. Handle replacement entries, mismatched directions, incomplete or malformed sequences, deterministic tie ordering, duplicate delivery, and bounded-state streaming follow-ups.

Company: Onepay

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: easy

Interview Round: Technical Screen

# Count Complete Highway Journeys from Toll Logs Each toll record is `(timestamp, plate, location, booth_type)`. `booth_type` is `ENTRY`, `MAINROAD`, or `EXIT`. The final character of `location` is the travel direction, `E` or `W`; the preceding integer is a mile marker. Implement `count_complete_journeys(records)` and return the number of valid completed journeys. A journey for one plate and direction starts with `ENTRY`, may contain zero or more `MAINROAD` records, and ends with `EXIT`. Records may be unsorted; process them by `(timestamp, original_input_index)`. A new `ENTRY` replaces any incomplete journey for the same plate. A `MAINROAD` or `EXIT` with no active journey, or with a direction different from the active journey, is ignored. A valid `EXIT` increments the count and clears that plate's active journey. ## Constraints - At most `200000` records. - Timestamps are non-negative numbers. - Plates and locations are non-empty strings. - A plate has at most one active journey at a time. ## Example The records below contain two complete journeys: ```text (1, "JOX304", "250E", ENTRY) (2, "THX138", "110E", ENTRY) (3, "JOX304", "270E", MAINROAD) (4, "JOX304", "280E", EXIT) (5, "THX138", "290E", EXIT) ``` ## Clarifications This task counts journeys only; no toll-rate or speed formula is supplied. Explain how state is isolated per plate and how malformed sequences are handled deterministically. ## Hints After sorting, one small state record per currently active plate is sufficient. ## Extensions - Compute distance or detect speeding when roadway metadata is provided. - Process an unbounded stream with bounded state. - Handle duplicate log delivery idempotently.

Quick Answer: Count completed highway journeys from unsorted entry, main-road, and exit toll records grouped by vehicle and direction. Handle replacement entries, mismatched directions, incomplete or malformed sequences, deterministic tie ordering, duplicate delivery, and bounded-state streaming follow-ups.

Each record is a four-element sequence `(timestamp, plate, location, booth_type)`. The entire list of records is passed as the single argument `records`. `booth_type` is `ENTRY`, `MAINROAD`, or `EXIT`. The final character of each non-empty `location` is the travel direction, `E` or `W`; the preceding integer is a mile marker. Return the number of valid completed journeys. Process records in ascending `(timestamp, original_input_index)` order, so records with equal timestamps keep their original order. State is isolated by plate, and a plate has at most one active journey. An `ENTRY` starts a journey in that record's direction and replaces any incomplete journey already active for the same plate. A `MAINROAD` record is accepted only when that plate has an active journey in the same direction; otherwise it is ignored. An `EXIT` completes and counts a journey only when the plate has an active journey in the same direction, then clears that plate's state. An `EXIT` or `MAINROAD` with no active journey is ignored. A journey may contain zero or more matching `MAINROAD` records. Mile markers do not affect this counting task.

Constraints

0 <= records.length <= 200000.
Each record contains exactly (timestamp, plate, location, booth_type).
Timestamps are non-negative numbers.
Plates and locations are non-empty strings.
Each location consists of an integer mile marker followed by E or W.
booth_type is ENTRY, MAINROAD, or EXIT.
A plate has at most one active journey at a time.

Examples

Input: ([(1, 'JOX304', '250E', 'ENTRY'), (2, 'THX138', '110E', 'ENTRY'), (3, 'JOX304', '270E', 'MAINROAD'), (4, 'JOX304', '280E', 'EXIT'), (5, 'THX138', '290E', 'EXIT')],)

Expected Output: 2

Explanation: The exact source example completes JOX304 after one MAINROAD record and THX138 with no MAINROAD record.

Input: ([],)

Expected Output: 0

Explanation: With no records, no plate can start or complete a journey.

Hints

Attach each record's original input index before sorting so equal timestamps remain deterministic.
Keep only the active direction for each plate; mile markers are not needed to count journeys.
Handle ENTRY replacement separately from MAINROAD and EXIT, which act only on a matching active direction.

Quick Overview