Implement a queue using two stacks. Recall that a queue is a FIFO (first-in, first-out) data structure with the following methods: enqueue, which inserts an element into the queue, and dequeue, which removes it.

daily-coding-problem-53.rb

#!/usr/bin/env ruby

class Queue 
    def initialize 
        @s1,@s2 = [],[]
    end 

    def enqueue e
        while not @s1.empty?
            @s2 << @s1.last() 
            @s1.pop()
        end
        @s1 << e
        while not @s2.empty? 
            @s1 << @s2.last() 
            @s2.pop() 
        end
    end 

    def dequeue 
        puts "Q is empty!" if @s1.empty? 
        @s1.pop() 
    end 

    alias << enqueue
    alias pop dequeue
end 

q = Queue.new()
q << 'e'
q << 'f'
q << 'g'
p q.pop()