Max Profit In Single Day Stock Prices

max_profit.rb

# There is an array stock_prices_yesterday where:
# * The indices are the time in minutes past trade opening time, which was 9:30am local time.
# * The values are the price in dollars of Apple stock at that time.
# For example, the stock cost $500 at 10:30am, so stock_prices_yesterday[60] = 500.

# Write an efficient algorithm for computing the best profit I could have made from 1 purchase and 1 sale of 1 Apple stock yesterday.

# No "shorting"—you must buy before you sell. You may not buy and sell in the same time step (at least 1 minute must pass).

def get_max_profit(stock_prices_yesterday)

    min_price = stock_prices_yesterday[0]
    max_profit = 0

    stock_prices_yesterday.each do |current_price|

        # ensure min_price is the lowest price we've seen so far
        min_price = [min_price, current_price].min

        # see what our profit would be if we bought at the
        # min price and sold at the current price
        potential_profit = current_price - min_price

        # update max_profit if we can do better
        max_profit = [max_profit, potential_profit].max
    end

    max_profit
end

stock_prices_yesterday = [500,200,600,100,150,155,156,158,159,163,160,200,300]
puts "Your max profit is #{get_max_profit(stock_prices_yesterday)}"