121.BestTimetoBuyandSellStock.py

"""
    Say you have an array for which the ith element is the price of a given 
    stock on day i.
    If you were only permitted to complete at most one transaction (i.e., buy 
    one and sell one share of the stock), design an algorithm to find the 
    maximum profit.
    Note that you cannot sell a stock before you buy one.

    Example:
    Input: [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.
                 Not 7-1 = 6, as selling price needs to be larger than buying 
                 price.

    Example:
    Input: [7,6,4,3,1]
    Output: 0
    Explanation: In this case, no transaction is done, i.e. max profit = 0.
"""
#Difficulty: Easy
#200 / 200 test cases passed.
#Runtime: 64 ms
#Memory Usage: 15.2 MB

#Runtime: 64 ms, faster than 80.54% of Python3 online submissions for Best Time to Buy and Sell Stock.
#Memory Usage: 15.2 MB, less than 33.70% of Python3 online submissions for Best Time to Buy and Sell Stock.

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        buy = float(inf)
        sell = 0
        for price in prices:
            buy = min(buy, price)
            sell = max(sell, price - buy)
        return sell