You are given an array `prices` where `prices[i]` is the price of a given stock on the `i`th day.
You want to maximize your profit by choosing a **single day** to buy one stock and choosing a **different day in the future** to sell that stock.
Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return `0`.
Example 1
Input:prices = [7,1,5,3,6,4]
Output:5
Explanation:Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Example 2
Input:prices = [7,6,4,3,1]
Output:0
Explanation:No transactions are done, max profit = 0.