Order Book Imbalance Signal

How this order book imbalance coding problem tests quant skills

This is a medium-difficulty Python coding problem that combines financial domain knowledge with practical algorithmic thinking. It appears regularly in interviews at quant trading firms because it requires you to implement a real market microstructure signal correctly—something researchers and traders build every day.

The problem tests your ability to handle a rolling-window calculation over a time series, manage edge cases (zero denominators in financial ratios), and translate a mathematical definition into clean, correct code. You'll need to decide whether to precompute all imbalances or stream them, and how to accumulate a rolling average efficiently without unnecessary recomputation.

• Rolling window aggregation and indexing
• Handling division by zero in financial metrics
• Time complexity trade-offs (naive sliding window vs. deque or prefix sums)
• Order book and market microstructure fundamentals

Interviewers typically follow up by asking how you would extend this to handle tick data with variable time intervals, or how you'd optimize if the window size k is very large relative to the input length.