121.py

# 121. Best Time to Buy and Sell Stock
# 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 1:

# 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 2:

# Input: [7,6,4,3,1]
# Output: 0
# Explanation: In this case, no transaction is done, i.e. max profit = 0.k

from typing import List


class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        minimum = float("inf")
        max_profit = 0
        for price in prices:
            if price < minimum:
                minimum = price
            elif (price - minimum) > max_profit:
                max_profit = price - minimum
        return max_profit


if __name__ == '__main__':
    from util import Test
    t = Test(Solution().maxProfit)
    t.equal(0, [7, 6, 4, 3, 1])