3. Best Time to Buy and Sell Stock
Given an array prices, return the maximum profit you can achieve from one buy and one sell.
範例 1:
輸入： prices = [7,1,5,3,6,4] 輸出： 5
範例 2:
輸入： prices = [7,6,4,3,1] 輸出： 0
限制條件：
1 <= prices.length <= 10^5
● 已自動儲存第 1 行，第 1 欄