Design an Order Book Class to Compute Exchange BBO and NBBO

You are given a stream of order records. Each record has: exchange_id: exchange identifier (string) price: price (integer) quantity: quantity (positive integer) order_type: side ("bid" or "ask") Implement a class OrderBook that supports: add(exchange_id, price, quantity, order_type): add one order record. get_exchange_bbo(exchange_id): return that exchange’s current BBO (Best Bid and Offer) as (best_bid, best_ask). best_bid is the highest bid price on that exchange, or None if no bids best_ask is the lowest ask price on that exchange, or None if no asks get_nbbo(): return the market-wide NBBO as (best_bid, best_ask). best_bid is the maximum of all exchanges’ best_bid, or None if no bids exist anywhere best_ask is the minimum of all exchanges’ best_ask, or None if no asks exist anywhere Notes/Constraints: quantity does not affect best price selection in this problem, but should be accepted/stored (for extensibility). Scale: up to N = 2 * 10^5 calls to add up to E = 10^4 exchanges Queries should be efficient; avoid scanning all historical orders on every query. Suggested I/O format for evaluation: Input: First line integer Q (number of operations) Next Q lines are one of: ADD exchange_id price quantity order_type EXBBO exchange_id NBBO Output: For each EXBBO and NBBO, print one line: best_bid best_ask (space-separated). Use string None for missing. Example Input 10 ADD NASDAQ 100 10 bid ADD NASDAQ 101 5 ask EXBBO NASDAQ NBBO ADD NYSE 99 7 bid ADD NYSE 102 2 ask NBBO ADD NASDAQ 98 1 bid ADD NASDAQ 97 1 ask NBBO Output 100 101 100 101 100 101 100 97