Practice/Stripe/Worker Task Assignment

Worker Task Assignment

CodingMust

Problem Overview

You are building a task assignment system for a support platform. The system needs to distribute incoming tasks to available workers based on various criteria that evolve across multiple parts of the problem.

The problem is divided into four progressive parts, each introducing additional complexity:

• Load Balancing: Assign tasks to workers based on current workload (least loaded first)
• Specialty Matching: Match tasks to workers who have the required specialty
• Account Affinity: Prioritize workers who have previously handled tasks from the same account
• Worker Availability: Handle workers going offline dynamically

Important Notes

• There are multiple parts to this problem -- ask the interviewer how many parts there are to better manage your time
• Start with the simplest data structure and extend it as parts get more complex
• Write your own test cases and ensure your code compiles and runs correctly

Part 1: Load Balancing

Implement a function assign_tasks(workers, tasks) that assigns each task to the worker with the least current workload.

Rules:

• Process tasks in the order they appear in the input
• Assign each task to the worker with the minimum total workload at that moment
• If multiple workers have the same workload, assign to the worker who appears first in the workers list
• A worker's workload increases by the task's duration when assigned a task

Example

workers = ["alice", "bob", "charlie"] tasks = [ {"id": "task1", "duration": 5}, {"id": "task2", "duration": 3}, {"id": "task3", "duration": 7}, {"id": "task4", "duration": 2}, {"id": "task5", "duration": 4}, ]

Output:

[ {"taskId": "task1", "worker": "alice"}, # all at 0, alice first in list {"taskId": "task2", "worker": "bob"}, # bob and charlie at 0, bob first {"taskId": "task3", "worker": "charlie"}, # charlie at 0 (lowest) {"taskId": "task4", "worker": "bob"}, # bob at 3 (lowest) {"taskId": "task5", "worker": "alice"}, # alice and bob tied at 5, alice first ]

Walkthrough:

• Initially all workers have workload 0. task1 goes to alice (first in list)
• alice: 5, bob: 0, charlie: 0. task2 goes to bob (first with minimum 0)
• alice: 5, bob: 3, charlie: 0. task3 goes to charlie (only one with 0)
• alice: 5, bob: 3, charlie: 7. task4 goes to bob (minimum workload 3)
• alice: 5, bob: 5, charlie: 7. task5 goes to alice (tied at 5, alice first in list)

Requirements

• Process tasks sequentially in input order
• Track cumulative workload per worker
• Use worker list order as tiebreaker
• Return assignments in task processing order

Part 2: Specialty Matching

Extend the system to handle workers with specialties. Each worker now has a specialty field, and each task has a list of requiredSpecialties. A task can only be assigned to a worker whose specialty matches one of the task's required specialties.

Among eligible workers (those with a matching specialty), assign to the one with the least workload (using the same tiebreaker rules as Part 1).

Example

` workers = [ {"name": "alice", "specialty": "billing"}, {"name": "bob", "specialty": "technical"}, {"name": "charlie", "specialty": "billing"}, {"name": "diana", "specialty": "technical"}, ]

tasks = [ {"id": "task1", "duration": 5, "requiredSpecialties": ["billing"]}, {"id": "task2", "duration": 3, "requiredSpecialties": ["technical"]}, {"id": "task3", "duration": 7, "requiredSpecialties": ["billing", "technical"]}, {"id": "task4", "duration": 2, "requiredSpecialties": ["billing"]}, {"id": "task5", "duration": 4, "requiredSpecialties": ["technical"]}, ] `

Output:

[ {"taskId": "task1", "worker": "alice"}, # billing: alice(0), charlie(0) -> alice first {"taskId": "task2", "worker": "bob"}, # technical: bob(0), diana(0) -> bob first {"taskId": "task3", "worker": "charlie"}, # all eligible: charlie(0) and diana(0) lowest, charlie first {"taskId": "task4", "worker": "alice"}, # billing: alice(5), charlie(7) -> alice lower {"taskId": "task5", "worker": "diana"}, # technical: bob(3), diana(0) -> diana lower ]

Requirements

• Filter workers by specialty before applying workload-based selection
• A task can be assigned to any worker whose specialty is in the task's requiredSpecialties list
• If no worker matches the required specialties, skip the task
• Continue using workload-based selection among eligible workers

Part 3: Account Affinity

Add account affinity to the assignment logic. Each task now has an accountId field. If a worker has previously handled a task from the same account, that worker should be prioritized for new tasks from that account.

Priority order:

1. Among eligible workers (matching specialty), prefer workers who have handled the same account before
2. Among workers with account affinity, choose the one with the least workload
3. If no worker has affinity, fall back to least workload among eligible workers
4. Use worker list order as the final tiebreaker

Example

` workers = [ {"name": "alice", "specialty": "billing"}, {"name": "bob", "specialty": "billing"}, {"name": "charlie", "specialty": "billing"}, ]

tasks = [ {"id": "task1", "duration": 5, "requiredSpecialties": ["billing"], "accountId": "acme"}, {"id": "task2", "duration": 3, "requiredSpecialties": ["billing"], "accountId": "globex"}, {"id": "task3", "duration": 7, "requiredSpecialties": ["billing"], "accountId": "acme"}, {"id": "task4", "duration": 2, "requiredSpecialties": ["billing"], "accountId": "acme"}, {"id": "task5", "duration": 4, "requiredSpecialties": ["billing"], "accountId": "globex"}, ] `

Output:

[ {"taskId": "task1", "worker": "alice"}, # no affinity yet; all at 0, alice first {"taskId": "task2", "worker": "bob"}, # no affinity; bob and charlie at 0, bob first {"taskId": "task3", "worker": "alice"}, # alice has acme affinity -> prioritized {"taskId": "task4", "worker": "alice"}, # alice still has acme affinity {"taskId": "task5", "worker": "bob"}, # bob has globex affinity ]

Walkthrough:

• task1 (acme): No one has handled acme yet. All at workload 0, alice first -> alice
• task2 (globex): No one has handled globex. alice: 5, bob: 0, charlie: 0 -> bob
• task3 (acme): alice handled acme before, so she is prioritized -> alice
• task4 (acme): alice still has acme affinity -> alice
• task5 (globex): bob handled globex before -> bob

Requirements

• Track which accounts each worker has handled
• Prioritize workers with account affinity over workload balancing
• If multiple workers have affinity for the same account, choose by lowest workload
• Fall back to Part 2 logic when no worker has affinity

Part 4: Worker Availability

Extend the system to handle workers going offline. Workers can become unavailable at any point, and the system must adapt.

New input: An additional parameter offline_events specifies when workers go offline:

offline_events = [ {"worker": "alice", "afterTaskIndex": 2} # alice goes offline after task index 2 ]

When a worker goes offline:

• They can no longer receive new task assignments
• Their account affinity data is preserved
• Tasks must be redistributed among remaining available workers

Example

` workers = [ {"name": "alice", "specialty": "billing"}, {"name": "bob", "specialty": "billing"}, {"name": "charlie", "specialty": "billing"}, ]

tasks = [ {"id": "task1", "duration": 5, "requiredSpecialties": ["billing"], "accountId": "acme"}, {"id": "task2", "duration": 3, "requiredSpecialties": ["billing"], "accountId": "globex"}, {"id": "task3", "duration": 7, "requiredSpecialties": ["billing"], "accountId": "acme"}, {"id": "task4", "duration": 2, "requiredSpecialties": ["billing"], "accountId": "acme"}, {"id": "task5", "duration": 4, "requiredSpecialties": ["billing"], "accountId": "globex"}, ]

offline_events = [ {"worker": "alice", "afterTaskIndex": 2} ] `

Output:

[ {"taskId": "task1", "worker": "alice"}, # alice gets acme (task index 0) {"taskId": "task2", "worker": "bob"}, # bob gets globex (task index 1) {"taskId": "task3", "worker": "alice"}, # alice has acme affinity (task index 2) # alice goes offline after task index 2 {"taskId": "task4", "worker": "charlie"}, # alice offline; charlie lowest workload (0) {"taskId": "task5", "worker": "bob"}, # bob has globex affinity ]

Requirements

• Track worker availability status
• Process offline events after the specified task index
• Skip unavailable workers during assignment
• Handle edge cases: all workers offline, no eligible workers available