Total traded volume per symbol

Question

You have a list of executed trades, each a (symbol, quantity) pair. Aggregate the total quantity per symbol and return the symbols ranked by total volume, largest first. Break ties alphabetically by symbol.

trades = [("AAPL", 100), ("MSFT", 50), ("AAPL", 30)]
-> [("AAPL", 130), ("MSFT", 50)]

Return the list of (symbol, total_volume) sorted by volume descending, ties broken by symbol ascending. Aim for $O(n \log n)$ .

Accepted Answer

Walk the trades once, summing quantities into a dictionary keyed by symbol. Then sort the dictionary items by a compound key: negative volume (so larger volume sorts first) and then the symbol (so ties resolve alphabetically). Tracing the example: AAPL accumulates 100 + 30 = 130, MSFT stays at 50. Sorting by descending volume gives [("AAPL", 130), ("MSFT", 50)]. Time O(n + u \log u) for u distinct symbols, space O(u). The tie-break key matters for deterministic output; negating the volume is the idiomatic way to sort one field descending while another stays ascending. Takeaway. Group-by-then-…

Total traded volume per symbol

Your answer

More Coding questions