Check to see if an array is already sorted?

Question

I know how to put an array in order, but in this case I just want to see if it is in order. An array of strings would be the easiest, I imagine, and answer

Answer 1

For this to work efficiently you will want to sort during insertion. If you are dealing with unique items, a SortedSet is also an option.

For clarification, if we patch array to allow for a sorted insertion, then we can keep the array in a sorted state:

class Array
  def add_sorted(o)
    size = self.size
    if size == 0
      self << o
    elsif self.last < o
      self << o
    elsif self.first > o
      self.insert(0, o)
    else
      # This portion can be improved by using a binary search instead of linear
      self.each_with_index {|n, i| if n > o; self.insert(i, o); break; end}
    end
  end
end

a = []
12.times{a.add_sorted(Random.rand(10))}
p a # => [1, 1, 2, 2, 3, 4, 5, 5, 5, 5, 7]

or to use the built in sort:

class Array
  def add_sorted2(o)
    self << o
    self.sort
  end
end

or, if you are dealing with unique items:

require "set"
b = SortedSet.new
12.times{b << Random.rand(10)}
p b # => #