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Problem · Design

Task Management System

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● Hard

AirbnbFULLTIMEOA

Problem statement

Implement a task-management service by processing a finite sequence of timestamped operations in order.

Every operation begins with an opcode. Timestamps are strictly increasing.

["ADD_USER", t, userId, quota] creates a user with a maximum number of active tasks.
["CREATE", t, taskId, userId, priority, dueAt, expiresAt] creates an active task. It fails if the task identifier already exists, the user does not exist, or the user's active-task quota is full.
["GET", t, taskId] returns [taskId, userId, priority, createdAt, dueAt, expiresAt, status], or an empty row for a missing or deleted task.
["UPDATE", t, taskId, priority, dueAt, expiresAt] updates an active task.
["DELETE", t, taskId] marks an existing non-deleted task as deleted.
["SEARCH", t, userId] returns that user's active task identifiers ordered by decreasing priority, then increasing creation timestamp, then identifier.
["SET_QUOTA", t, userId, quota] changes a user's quota. Lowering it does not remove existing tasks, but new tasks remain blocked until the active count is below the quota.
["COMPLETE", t, taskId] marks an active task completed.
["HISTORY", t, userId, view] returns identifiers in increasing creation order. view is COMPLETED, EXPIRED, UNFINISHED, or OVERDUE. Unfinished tasks are active; overdue tasks are active tasks with dueAt < t.

Before each operation at time t, every active task with expiresAt <= t becomes expired. Completion, deletion, and expiration free an active-task quota slot.

Return one row per input operation. State-changing operations return ["OK"] on success. Failures return one of ["UNKNOWN_USER"], ["DUPLICATE_TASK"], ["QUOTA_EXCEEDED"], ["NOT_FOUND"], or ["NOT_ACTIVE"]. Search and history operations may return an empty row.

Function

processTaskOperations(operations: String[][]) → String[][]

Examples

Example 1

operations = [["ADD_USER","1","u1","2"],["CREATE","2","t1","u1","5","10","20"],["CREATE","3","t2","u1","7","4","30"],["SEARCH","5","u1"],["COMPLETE","6","t2"],["HISTORY","7","u1","COMPLETED"],["SET_QUOTA","8","u1","1"],["CREATE","9","t3","u1","9","12","40"],["GET","20","t1"]]return = [["OK"],["OK"],["OK"],["t2","t1"],["OK"],["t2"],["OK"],["QUOTA_EXCEEDED"],["t1","u1","5","2","10","20","EXPIRED"]]

The higher-priority task is returned first. Completing it frees a quota slot, but the later quota reduction leaves one active task, so the next creation is rejected. The final read first expires t1.

Constraints

1 <= operations.length <= 200000
All timestamps and task time fields are integers in [0, 10^9]; operation timestamps are strictly increasing.
For every CREATE or UPDATE, operation timestamp < dueAt < expiresAt.
User and task identifiers are nonempty ASCII strings of at most 40 characters.
Priority is an integer in [-10^9, 10^9]; quota is in [0, 200000].
ADD_USER uses a new user identifier. SET_QUOTA, SEARCH, and HISTORY name an existing user.
The total number of task records examined by all SEARCH and HISTORY operations is at most 200000.