Each method should run in constant time. Implement a stack that has the following methods:

daily-coding-problem-43.rb

#!/usr/bin/env ruby


class Stack 
    def initialize(init=nil)
        @stack = []
        @stack << init if !init.nil?
    end 
    def push val 
        @stack << val
    end  
    alias << push
    def pop 
        return nil if @stack.empty?
        return @stack.pop()
    end 
    def max 
        return nil if @stack.empty?
        return @stack.max()
    end 
    def to_s
        return @stack.to_s
    end 
end 

stack = Stack.new() 
stack << '1'
stack << '2'
puts stack.to_s