[LeetCode] Best Time to Buy and Sell Stock

문제

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.

예제

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.

조건

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

답

풀이 1

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        ans = 0
        buy = prices[0]
        
        for i in range(1, len(prices)):
            if prices[i] <= buy:
                buy = prices[i]
            else:
                ans = max(ans, prices[i] - buy)
        
        return ans

풀이 2

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        profit = 0
        min_price = int(1e9)
        
        for price in prices:
            min_price = min(min_price, price)
            profit = max(profit, price - min_price)
        
        return profit