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121. Best Time to Buy and Sell Stock

Easy

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:

To solve the “Best Time to Buy and Sell Stock” problem in Python with a Solution class, we’ll use a greedy algorithm. Below are the steps:

  1. Create a Solution class: Define a class named Solution to encapsulate our solution methods.

  2. Create a maxProfit method: This method takes an array prices as input and returns the maximum profit that can be achieved by buying and selling the stock.

  3. Initialize variables: Initialize two variables, minPrice to store the minimum price seen so far and maxProfit to store the maximum profit seen so far. Initialize maxProfit to 0.

  4. Iterate through the prices array:
    • For each price in the array:
      • Update minPrice to the minimum of the current price and minPrice.
      • Update maxProfit to the maximum of the current profit (price - minPrice) and maxProfit.
  5. Return the maximum profit: After iterating through the entire array, return maxProfit.

Here’s the Python implementation:

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        min_price = float('inf')
        max_profit = 0

        for price in prices:
            if price < min_price:
                min_price = price
            elif price - min_price > max_profit:
                max_profit = price - min_price

        return max_profit

This implementation follows the steps outlined above and efficiently calculates the maximum profit that can be achieved by buying and selling the stock in Python.

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