My first instinct was to reach for something fancy and I wasted a couple minutes thinking about it before realizing this is just a hashmap and a loop.
Start by clarifying the problem constraints and edge cases, then propose a solution using a hash map to track balances and a list for rejected transactions. Walk through the algorithm step by step, emphasizing the overdraft check and final filtering of non-zero balances. Discuss time and space complexity, and consider potential optimizations or trade-offs.
Pro tip: Mention that you would handle edge cases like self-transactions, zero-amount transactions, and duplicate user IDs, and discuss how the solution scales with large transaction volumes. This shows attention to detail and production readiness.
Ask questions to confirm assumptions: Are user IDs strings or integers? Can transactions be zero or negative? Should rejected transactions preserve original order? How to handle self-transfers?
Use a hash map to store balances for each user (default 0) and a list to collect rejected transactions. Consider if any additional structures are needed for efficiency.
Iterate through each transaction: check if sender's balance minus amount is >= 0. If yes, update balances; if no, add to rejected list. Ensure sender and receiver are initialized in the map if not present.
After processing, filter the balance map to include only users with non-zero balances. Return the rejected transactions and the filtered balances.
Discuss time complexity O(n) and space O(u + r) where u is unique users and r is rejected transactions. Mention alternative approaches like sorting or batch processing and their trade-offs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.