動機

經典的stock系列題目的開始

Problem

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: 5Explanation: 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: 0Explanation: In this case, no transactions are done and the max profit = 0.

 

Constraints:

  • 1 <= prices.length <= 105
  • 0 <= prices[i] <= 104

Sol

只能做一次就從最小的去算

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        small = math.inf
        ret = 0
        for p in prices:
            small = min(small, p)
            ret = max(ret, p-small)
        return ret