Here's the solution I came up with for this interview question on interviewcake.com: "Write a function to reverse a string in place. 'In place' means 'without creating a new string in memory.'" http://www.interviewcake.com/question/reverse-string-in-place

reverso.rb

# `ruby reverso.rb "foo"`
class Reverso
    def initialize
        my_arr = ARGV[0].split("")
        puts "'#{self.reverso(my_arr)}'"
    end

    def reverso my_arr
        len = my_arr.size - 1
        halflen = ((len + 1)/2.0).ceil
        i = 0
        temp = ""

        my_arr.each do |c|

            return my_arr.join if i === halflen

            replaco(my_arr, i, len)

            len-=1
            i+=1

        end
    end

    def replaco my_arr, i, len
        temp = my_arr[i]
        my_arr[i] = my_arr[len]
        my_arr[len] = temp
    end
end

@reverso = Reverso.new