[121. Best Time to Buy and Sell Stock] #leetcode

121_1015.py

class Solution(object):
    def maxProfit(self, prices):
        """
        :type prices: List[int]
        :rtype: int
        """
        # O(n) O(1)
        # for each price points, we want to know the lowest price before and 
        # then we can get the max profit
        
        # corner case
        if not prices:
            return 0
        
        # initial min price and max profit
        min_price = prices[0]
        max_profit = 0
        
        # loop price
        for price in prices:
            min_price = min(min_price, price)
            max_profit = max(max_profit, price - min_price)
            
        # return 
        return max_profit