Tracker for top tickers by cumulative volume

Design a class that ingests a stream of trades and supports two operations: execute_trade(ticker, volume) records a trade, and most_traded(k) returns the $k$ tickers with the largest total volume as strings of the form TICKER VOLUME. For example, after trades TSLA 1000, NFLX 700, TSLA 200 and META 1400, asking for the top $2$ should give META 1400 then TSLA 1200. Explain your design and complexities.

A hash map of totals plus a size-$k$ min-heap at query time. execute_trade adds the volume to the ticker's running total in $O(1)$. most_traded(k) pushes each of the $n$ tickers into a min-heap capped at $k$ (popping the smallest when it overflows), then sorts the survivors descending: $O(n\log k)$ time, $O(n)$ storage. If queries dominate, keep a balanced tree keyed by volume instead.