apple_stock.rb

# swap loops so we can exit early from the inner loop once we've searched the valid range

require "pp"
require "minitest/autorun"

class StockTest < Minitest::Test
  attr_accessor :loops
  
  def pick_best_time_to_buy(stock)
    best_value = 0
    best_buy_index = 0
    best_sell_index = 0
    
    stock.each_with_index  do |sell_price, sell_index|
      stock.each_with_index do |buy_price, buy_index|
        break if buy_index >= sell_index 
      
        value = sell_price - buy_price
        next if value < best_value

        best_value = value
        best_buy_index = buy_index
        best_sell_index = sell_index
      end
    end  
    
    {value: best_value, buy_index: best_buy_index, sell_index: best_sell_index}
  end
  
  def test_picking_best_time_to_buy
    stock = [1,8,3,0,1,54,29,1,3,10,49,10,39,28,41,1,3]
    
    max = pick_best_time_to_buy(stock)

    assert_equal 3, max[:buy_index]
    assert_equal 5, max[:sell_index]
    assert_equal 54, max[:value]
  end  
end