You have been tasked with creating an exchange where traders can buy and sell Sea Shells. The program reads incoming orders and emits trades.
Input (stdin) – the input is a stream of limit orders. Each line is a separate order identified by its line number (starting at 1), with space-delimited fields:
- the string
"limit" - side:
"buy"or"sell" - volume (integer): positive number of Sea Shells to trade
- price (decimal): a positive price limit with two decimals (e.g., 99.50)
Examples:
limit buy 10 55.30
limit sell 5 57.12
Processing orders
- Incoming limit orders are matched against previously booked orders of the opposite side. Each match emits a trade.
- Matching continues until the incoming order is completely filled or there are no further matches. Any unfilled remainder of the incoming order is booked for future matching.
- Orders are processed in arrival order; order k must finish executing before k+1 executes.
Matching rules
- Prices must be compatible:
- A sell may match highest priced buys first, at or above the sell’s price.
- A buy may match lowest priced sells first, at or below the buy’s price.
- Tie-breakers: if multiple resting orders have the same best price, match the oldest first (FIFO at each price level).
Executing trades / Output (stdout)
For each match, output a line:
match <incoming_order_id> <resting_order_id> <traded_volume> <price>
Example
Input:
limit buy 10 99.00
limit buy 15 100.00
limit buy 3 100.50
limit sell 5 100.00
limit buy 5 99.50
Output:
match 4 3 3 100.50
match 4 2 2 100.00
Brief summary: Build a price-time priority limit order book. For each incoming order, repeatedly match against the best-priced opposite orders (best price, then FIFO), emit match lines for fills, and book any remainder. Core data structures: price-sorted maps per side with FIFO queues per price.
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