Best Time to Buy and Sell Stock

You are given an array prices where prices[i] is the price of a stock on day i.

You want to maximize your profit by choosing a single day to buy and a later day to sell. Return the maximum profit you can achieve. If no profit is possible, return 0.

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Example 1

Input: prices = [7, 1, 5, 3, 6, 4]
Output: 5
Explanation: Buy on day 2 (price = 1), sell on day 5 (price = 6). Profit = 6 - 1 = 5.

Example 2

Input: prices = [7, 6, 4, 3, 1]
Output: 0
Explanation: Prices only decrease; no transaction is profitable, so return 0.

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Constraints

• 1 <= prices.length <= 10^5
• 0 <= prices[i] <= 10^4