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Design crypto trading order control API

CoinbaseSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenCoding & Algorithms

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This question evaluates understanding of state management and finite-state machines, API design for lifecycle control, and implementation of in-memory data structures and transition validation in the Coding & Algorithms category.

You are implementing part of a simple crypto trading system that manages client orders. Each order can be in one of several states: NEW, ACTIVE, PAUSED, CANCELLED, or FILLED.

You need to support the following operations for a single order (you can assume order creation is already done):

  1. pause(orderId): Temporarily pause an active order so that it will not be matched or executed while paused.
  2. resume(orderId): Resume a paused order so that it becomes active again and can be matched.
  3. cancel(orderId): Cancel an order so that it will never be executed in the future.

Rules and constraints:

  • Valid state transitions are:
  • NEW -> ACTIVE
  • ACTIVE -> PAUSED
  • PAUSED -> ACTIVE (on resume)
  • ACTIVE -> CANCELLED
  • PAUSED -> CANCELLED
  • ACTIVE -> FILLED
  • Once an order is in CANCELLED or FILLED, no further operations (pause, resume, or cancel) should change its state.
  • pause on a non-ACTIVE order should be rejected.
  • resume on a non-PAUSED order should be rejected.
  • cancel on a CANCELLED or FILLED order should be a no-op or return an error (choose one behavior and be consistent).

Implement a small in-memory component that:

  • Stores the current state of each order by orderId.
  • Exposes methods pause, resume, and cancel that update state according to the rules above.
  • Returns success/failure for each operation based on whether the transition is allowed.

Describe your data structures and implement the core logic for these operations.