Stack class with built in min value

gistfile1.rb

class Stack
  
  def initialize
    @main = []
    @min  = []
  end
  
  def push val
    @main << val
    
    @min << val if val <= min
    
    val
  end
  
  def pop
    val = @main.pop
    
    @min.pop if min == val
    
    val
  end
  
  def min
    @min.last
  end
  
end