Implement a crypto order management system

Q: Implement a crypto order management system

This question evaluates data-structure design, command parsing, state-management, and error-handling competency for implementing an in-memory order management system, and is categorized under Coding & Algorithms with a practical application focus emphasizing efficient query support.

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Question

You are building an in-memory crypto order management system. You must parse commands from standard input and print outputs for query commands.

Order model

Each order has:

orderId (string, unique)
symbol (string, e.g., BTC-USD )
side ( BUY or SELL )
qty (positive integer)
state ∈ {LIVE, PAUSED, CANCELLED}

New orders start in state LIVE.

Input

A sequence of newline-separated commands. Your program should ignore blank lines.

Commands

CREATE <orderId> <symbol> <side> <qty>
- Creates a new order. If orderId already exists, treat it as an error (see Errors ).
PAUSE <orderId>
- If the order exists and is LIVE , change it to PAUSED .
RESUME <orderId>
- If the order exists and is PAUSED , change it back to LIVE .
CANCEL <orderId>
- If the order exists and is not already CANCELLED , change it to CANCELLED .
GET <orderId>
- Print the current state as: <orderId> <state> .
COUNT <state>
- Print how many orders are currently in that state as a single integer.

Errors

For invalid commands or invalid transitions (e.g., RESUME on a LIVE order, or referencing an unknown orderId), print:

ERROR

(You may assume command tokens are space-separated.)

Output

Print one line per GET and COUNT command, and also one line (ERROR) for each command that errors.

Constraints

Up to 200,000 commands.
orderId length ≤ 64.

Notes

Design your data structures so that GET and COUNT are efficient, and state transitions do not require scanning all orders.