## DEV Community

Arjun Rajkumar

Posted on • Updated on

# Write better code: Day 1 - Apple Stock Prices

This post originally appeared on Arjun Rajkumar's blog. Arjun is a web developer based in Bangalore, India.

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### Day 1: Question 1

Write an efficient method that takes stock_prices and returns the best profit you could have made from one purchase and one sale of one share of Apple stock yesterday.

For example:

stock_prices = [10, 7, 5, 8, 11, 9]

get_max_profit(stock_prices)
# returns 6 (buying for \$5 and selling for \$11)

No "shorting"—you need to buy before you can sell. Also, you can't buy and sell in the same time step—at least 1 minute has to pass.

Question from InterviewCake

Arjun Rajkumar • Edited

This was my logic for doing this.

Logic:

• Go thru each price one by one.
• See if the current stock is lesser than previous min_stock stored variable.
• See if the profit is greater than max profit stored. (max_profit, pot_profit)
• Going thru the loop once so it is O[n] time
• O[1] space as storing fixed.

It works with these few example cases:
Examples: [10, 7, 5, 8, 11, 9] -> 6 ; [10, 7, 100, 8, 11, 9] -> 92 ; [10] -> 0 ; [10, 2] -> 0.

Code:

Github

M Bellucci • Edited

In ruby