Figure out the optimal buy and sell point for a given stock, given its prices yesterday. No "shorting"—you need to buy before you can sell.

buy_low_sell_high.py

def buy_low_sell_high(lst):
    """Figure out the optimal buy and sell point for a given stock, given its prices yesterday.
    No "shorting"—you need to buy before you can sell. """

    min_buy = lst[0]
    mx_gain = 0

    for i in range(len(lst)):
        if lst[i] - min_buy >= mx_gain:
            mx_gain = lst[i] - min_buy
        if lst[i] <= min_buy:
            min_buy = lst[i]

    return mx_gain


print(buy_low_sell_high([10, 7, 5, 8, 11, 9]))  # 5 & 11 = 6
print(buy_low_sell_high([12, 10, 7, 3, 4, 33, 4, 8]))  # 3 & 33 = 30
print(buy_low_sell_high([30, 20, 10, 5]))  # 0 gain
print(buy_low_sell_high([5, 10, 33, 4, 7]))  # 5 & 33 = 28