121. Best Time to Buy and Sell Stock

Problem Statement

link: https://leetcode.com/problems/best-time-to-buy-and-sell-stock/ https://leetcode.cn/problems/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:

Input: prices = [7,1,5,3,6,4] Output: 5

Input: prices = [7,6,4,3,1] Output: 0

Solution Approach

The key to solving this problem lies in finding the minimum price to buy the stock and the corresponding maximum price difference to sell the stock.

Algorithm

1. Initialize min_buy with the first price.
2. Traverse through prices; if a lower price is found, update min_buy. Otherwise, calculate profit and update max_profit if it’s higher.
3. Return max_profit at the end.

Implement

    def maxProfit(self, prices: List[int]) -> int:
      min_buy = prices[0]
      max_profit = 0
      for p in prices[1:]:
          if p < min_buy:
              min_buy = p
          else:
              max_profit = max(max_profit,p - min_buy)
      return max_profit
          

    
    

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