0121-best-time-to-buy-and-sell-stock

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Description

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:

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

Solution(Python)

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        # min_ max_
        # check min_
        # num > max_
        min_ = float('inf')
        res = 0
        for price in prices: # 3,2,6,5,0,3
            if price < min_: 
                min_ = price # min_ = 0
                max_ =  price # max_ = 0
            elif price >= max_: 
                max_ =  price # max_ = 3
                res = max(res, max_ - min_) # res = 3
        return res