maxdiff.rb

=begin

A simple algorithm, not the most efficient*, can be explained as:

Iterate through every element in the array; call the current one "outer":
  For every element after "outer", Step through and compare to "outer"
    If the difference is larger than previously compared, store the result.
At the end, show the largest difference.

I read up on a few more advanced algorithms that should be more efficient, 
however I managed to break the two I tried fairly easily. So I sticking with 
simple.

=end

stock = [5, 6, 4, 7, 9, 8, 8, 11, 2]

difference = 0
minimum = 0

(0..stock.length - 1).each do |outer|
  (outer + 1..stock.length - 1).each do |inner|
    if stock[inner] - stock[outer] > difference then
      difference = stock[inner] - stock[outer]
      minimum = stock[outer]
    end
  end
end

puts "Best to buy the stock at #{minimum}, sell it at $#{minimum + difference}, for a profit of $#{difference}"