stock_picker.rb

def stock_picker(arr)
  max_value = arr[1]
  min_value = arr[0]
  best_day_to_buy = 0
  best_day_to_sell = 0

  arr.each_with_index do |v, i|
    if max_value < v && i > 0
      max_value = v
      best_day_to_sell = i
    end 
  end

  arr.each_with_index do |v, i|
    if min_value > v && i < best_day_to_sell
      min_value = v
      best_day_to_buy = i
    end
  end

  p [best_day_to_buy, best_day_to_sell]
  puts "For a profit of: $#{max_value - min_value}"
end

stock_picker([18, 3, 6, 9, 15, 18, 6, 9, 1])