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:
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Track the minimum price seen so far and the maximum profit. For each price, calculate the profit if we sell at that price (current price - minimum price). Update the maximum profit if this profit is greater.