CodingForInterviews.com Feb 20, 2013 Article

gistfile1.rb

# Binary Search
def search array, num, first, last
  middle = (first+last)/2
  if (first or last) == middle
    return -1
  end
  if num == array[middle]
    return middle
  elsif num > array[middle]
    search(array, num, middle, last)
  elsif num < array[middle]
    search(array, num, first, middle)
  end  
end

array = [-10, -2, 1, 5, 5, 8, 20]
result = search(array, 5, 0, array.length)
puts result

# Singleton Implementation.
class MySingleton

  attr_accessor :lock_enabled

  def initialize
    @lock_enabled = false
  end

  # Class Variable
  @@singleton = MySingleton.new

  def self.instance
    return @@singleton
  end

  # Ensure we the user can't call new themselves.
  private_class_method :new
end


# Very basic example of how we could use a Singleton
# class.
class MySuperAwesomeProject

  def writeStuff
    unless MySingleton.instance.lock_enabled
      MySingleton.instance.lock_enabled = true
      return true # We can write stuff!
    else
      return false # We can't write stuff :-(
    end
  end

  def doneWritingStuff
    MySingleton.instance.lock_enabled = false
  end

end

ap = MySuperAwesomeProject.new

puts ap.writeStuff   # True
puts ap.writeStuff   # False
ap.doneWritingStuff
puts ap.writeStuff   # True

# TJ Biddle
# biddle.thomas at gmail dot com
# SF, CA