max profit

def solution(a)
    @top_gain = 0
    
    a.each_with_index do |price, day|

        if day == 0
            @bottom = price
            @top = price
        end

        if price > @top
            @top = price 
        end
        
        if price < @bottom
            @bottom = price
        end
        
        possible_gain = price - @bottom 
    
        if possible_gain > @top_gain
            @top_gain = possible_gain
        else
            if price < @bottom                
                @bottom = price                 
            end
        end
    end
    
    @top_gain
   
end