121. Best Time to Buy and Sell Stock

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

Best Time to Buy and Sell Stock - LeetCode

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

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

• 리스트를 앞에서부터 하나씩 보면서, 제일 작은 애만 찾는다.
• 리스트 요소 하나씩 보면서 그동안 제일 작은 놈과 차를 계산하여, 그 위치까지의 가장 큰 이득을 구한다.
• 다른 사람들의 코드를 봤을 때, 더 많은 변수와 if문을 사용하고 있었기 때문에, 내 코드가 가장 깔끔한 것 같다.