Key Definitions

• User: identified uniquely by userId.
• Stock: identified uniquely by symbol; has a current price.
• Wallet: each user has a wallet balance used to buy stocks; selling stocks adds money back to the wallet.
• Portfolio: a user’s holdings (quantity per stock symbol).
• Available stocks: the set of stocks added by admins; users can trade only from this set.

Method Signatures

Constructor

BuyStocks()

• Initializes an empty platform with no users and no stocks.

User Signup

boolean signUp(String userId, String name, int initialWalletAmount)

• userId is always unique and non blank.
• 1 < initialWalletAmount < 900,000
• Returns true if the user is created. otherwise do nothing and return false if called with a duplicate or blank userId.

Admin Stock Management

boolean adminAddOrUpdateStock(String symbol, int price)

• Adds a new stock to the available list, or updates the price for an existing stock.
• Returns true if the stock is added/updated; otherwise false.
• 0 < price < 100,000
• Symbol contains [A-Z] and - (hyphen)

List<String> listAvailableStocks()

• Returns the list of available stocks as strings in the format: "SYMBOL PRICE".
• The returned list must be sorted lexicographically by SYMBOL for deterministic output.

Trading

boolean buyStock(String userId, String symbol, int quantity)

• 1≤ quantity < 10,000.
• User must exist and symbol must be in the available stock list.
• Trade executes at the current stock price.
• Returns false if the wallet balance is insufficient, or inputs are invalid.
• Returns true and updates wallet + portfolio on success.

boolean sellStock(String userId, String symbol, int quantity)

• quantity > 0.
• User must exist and must own at least quantity shares of symbol.
• Trade executes at the current stock price.
• Returns false if holdings are insufficient, or inputs are invalid.
• Returns true and updates wallet + portfolio on success.

Wallet and Portfolio Views

int getWalletBalance(String userId)

• Returns the user’s wallet balance.
• Returns -1 if userId does not exist.

List<String> getPortfolio(String userId)

• Returns the user’s holdings as strings in the format: "SYMBOL QUANTITY".
• Include only symbols with QUANTITY > 0.
• The returned list must be sorted lexicographically by SYMBOL for deterministic output.
• Returns an empty list if the user exists but holds no stocks.
• Returns an empty list if userId does not exist.

Constraints

• 1 <= userId.length() <= 30, 1 <= name.length() <= 60
• 1 <= symbol.length() <= 10
• All operations must run in-memory with efficient lookups (e.g., maps/dictionaries).

Notes

• If a method returns false, the system state must remain unchanged for that operation.
• All outputs that are lists must be deterministic (sorted as specified).
• All prices and wallet amounts are integers (no decimals).

Examples

Example 1: Basic signup, buy, sell, and views

• BuyStocks() → (constructor)
• adminAddOrUpdateStock(symbol="AAPL", price=100) → true
• adminAddOrUpdateStock(symbol="TSLA", price=250) → true
• signUp(userId="u1", name="Asha", initialWalletAmount=1000) → true
• buyStock(userId="u1", symbol="AAPL", quantity=5) → true
• getWalletBalance(userId="u1") → 500
• getPortfolio(userId="u1") → ["AAPL 5"]
• sellStock(userId="u1", symbol="AAPL", quantity=2) → true
• getWalletBalance(userId="u1") → 700
• getPortfolio(userId="u1") → ["AAPL 3"]
• listAvailableStocks() → ["AAPL 100", "TSLA 250"]

Example 2: Invalid operations and deterministic lists

• BuyStocks() → (constructor)
• adminAddOrUpdateStock(symbol="GOOG", price=300) → true
• adminAddOrUpdateStock(symbol="AMZN", price=200) → true
• listAvailableStocks() → ["AMZN 200", "GOOG 300"]
• signUp(userId="u2", name="Ravi", initialWalletAmount=250) → true
• signUp(userId="u2", name="Ravi Again", initialWalletAmount=999) → false
• buyStock(userId="u2", symbol="NFLX", quantity=1) → false
• buyStock(userId="u2", symbol="GOOG", quantity=1) → false
• buyStock(userId="u2", symbol="AMZN", quantity=1) → true
• getWalletBalance(userId="u2") → 50
• getPortfolio(userId="u2") → ["AMZN 1"]
• sellStock(userId="u2", symbol="AMZN", quantity=2) → false
• sellStock(userId="u2", symbol="AMZN", quantity=1) → true
• getWalletBalance(userId="u2") → 250
• getPortfolio(userId="u2") → []
• getWalletBalance(userId="unknown") → -1
• getPortfolio(userId="unknown") → []