# 121 Best Time to Buy and Sell Stock

You are given an array `prices` where `prices[i]` is the price of a given stock on the `ith` 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.
Note that buying on day 2 and selling on day 1 is not allowed
because you must buy before you sell.
``````

Example 2:

``````Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.
``````

Constraints:

• `1 <= prices.length <= 105`
• `0 <= prices[i] <= 104`
 `````` 1 2 3 4 5 6 7 8 9 10 `````` ``````class Solution: def maxProfit(self, prices: List[int]) -> int: lowest = math.inf max_profit = 0 for p in prices: if p < lowest: lowest = p else: max_profit = max(max_profit, p - lowest) return max_profit``````