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Concert Ticket Exchange
Programming challenge description:
Concert tickets can be hard to come by, especially when going through the resale market. We would like to build our own concert ticket exchange system so that we can view available tickets in real-time. This system will listen to incoming ticket orders for a new concert venue, BT Arena. We'd like to build a system that listens to concert ticket orders and provides fans with this market information in the form of a price ladder.

Concert ticket orders arrive as a stream of events that can either add an order to our market data book or delete an order from our book. We also want to be able to delete all orders at given price level.

Add orders come with the following information:

Action - ADD
OrderId - unique identifier for order
Artist - concert performer, such as "TaylorSwift" or "Drake"
Price - price for the order
Quantity - positive quantity is a buy order and negative quantity is a sell order
Delete orders come with the following information:

Action - DEL
Artist - concert performer, such as "TaylorSwift" or "Drake"
OrderId - Unique identifier for the order to be deleted
Delete price levels come with the following information:

Action - DEL_PRICE
Artist - concert performer, such as "TaylorSwift" or "Drake"
Price - price level to be deleted
We'd like to keep track of these events so that fans can request a market view in the form of a price ladder. A price ladder is made up of n price levels for buy orders and sell orders. A price level consists of the Price, BuyQuantity, and SellQuantity. A price level will either have a non-zero BuyQuantity or SellQuantity, but not both. For buy orders, the best price is the highest price because that is the price a ticket holder would sell at. Conversely, the best price for sell orders is the lowest price. The streamed events will guarantee at least n price levels for both buys and sells.

Input:
Repeated number of order operations in the following format:

<ADD> <OrderId> <Artist> <Price> <Quantity>
<DEL> <OrderId> <Artist>
<DEL_PRICE> <Artist> <Price>

We can get orders for different artists in the same stream of operations. The last line of input will the artist and number of price levels that we would like to view in our ladder for both buy and sell orders.

<Artist> <NumberOfPriceLevels>

Example Input:

ADD 1 TaylorSwift 100 10
ADD 2 TaylorSwift 101 -10
ADD 3 TaylorSwift 99 5
ADD 4 TaylorSwift 102 -5
ADD 5 TaylorSwift 100 2
ADD 6 Drake 95 2
DEL 1 TaylorSwift
TaylorSwift 2

Output:
The price ladder should begin with the artist name and should be followed by a repeated list of levels.

<Artist>
<BuyQuantity> <Price> <SellQuantity>

The levels should be sorted by price in descending order and contain NumberOfPriceLevels for buy and sell orders. Levels with 0 BuyQuantity and 0 SellQuantity should not be printed.

Example Output:

TaylorSwift
0 102 5
0 101 10
2 100 0
5 99 0

Test 1
Test Input
Download Test 1 Input
ADD 1 TaylorSwift 100  10
ADD 2 TaylorSwift 101 -10
ADD 3 TaylorSwift 99   5
ADD 4 TaylorSwift 102 -5
ADD 5 TaylorSwift 100  2
DEL 1 TaylorSwift
TaylorSwift 2
Expected Output
Download Test 1 Output
TaylorSwift
0 102 5
0 101 10
2 100 0
5 99 0
Test 2
Test Input
Download Test 2 Input
ADD 1 TaylorSwift 100  10
ADD 2 TaylorSwift 101 -10
ADD 3 TaylorSwift 99   5
ADD 4 TaylorSwift 102 -5
ADD 5 TaylorSwift 98 2
ADD 6 TaylorSwift 99   5
DEL_PRICE TaylorSwift 100
TaylorSwift 1
Expected Output
Download Test 2 Output
TaylorSwift
0 101 10
10 99 0