## Problem Given daily stock prices, choose at most one buy followed by at most one sell and return the maximum possible profit. The sale must occur on a later day than the purchase. Return `0` when no profitable trade exists. ### Function Contract Implement `maxSingleTradeProfit(prices)` and return one integer. ### Constraints & Assumptions - `0 <= len(prices) <= 200,000`. - `0 <= prices[i] <= 10^9`. - You may hold at most one share. - Transaction fees and taxes are ignored. ### Clarifying Questions to Ask - May the stock be sold before it is bought? No. - Is doing nothing allowed? Yes, yielding profit `0`. - Are multiple transactions allowed? No. ```hint Keep the best purchase seen so far While scanning from left to right, compare today's price with the minimum earlier price, then update the minimum for future days. ``` ### Examples ```text [7,1,5,3,6,4] -> 5 [7,6,4,3,1] -> 0 [2,4,1] -> 2 ``` ### Evaluation Focus - Preserves buy-before-sell order. - Returns zero for descending, empty, or single-price inputs. - Runs in `O(n)` time and `O(1)` auxiliary space. ### Extensions to Discuss 1. How would you return the buy and sell indices? 2. What changes if unlimited nonoverlapping transactions are allowed? 3. How would a transaction fee affect the state?