Merge Sort - Ruby

#! /usr/bin/env ruby
class Array
    def mergesort

        return self if length <= 1

        if length == 2 # we swap if the length is two and the "two array" is unsorted still
            if (self[0] > self[1])
                self[0],self[1] = self[1],self[0]
            end

            return self
        end

        left = self[0...self.length/2].mergesort
        right = self[self.length/2...self.length].mergesort

        arr = []

        while(!left.empty? && !right.empty?)
            if left.first < right.first
                arr << left.first
                left.shift #i remove the first element from left after it gets merged
                # it's so i can keep comparing using left/right.first
            else
                arr << right.first
                right.shift # remove first element from right after merging it
            end
        end

        if !left.empty?
            arr += left # if the left array is not yet fully merged, tack on the remaining values
        elsif !right.empty?
            arr += right # if the right array is not yet fully merged, tack on remaining values
        end

        return arr
    end
end




puts "give me a string"
str = gets.chomp.split('')
strlen = str.length
puts str.mergesort.join('')