swap_once.rb

#
# Check if an Array could be sorted by One-Swap.
#

# Extend Array Class...
class Array
  def sorted?
    # each_cons(2).all? { |a, b| (a <=> b) <= 0 }
    self == self.sort
  end

  def swap(i, j)
    self[i], self[j] = self[j], self[i]
  end
end


# Example Arrays...
A = [1, 5, 3, 3, 7]
B = [1, 3, 5, 3, 4]
C = [1, 3, 5]


# The code.......................

def sortable_by_one? a
  # 1 . already sorted ?
  if a.sorted?
    puts "Array is already sorted!"
    return true
  end

  # 2 . sorted by one move ?
  size = a.size

  (0...size).each_cons(2) do |i, sw|
    (sw...size).each do |sw|
      puts " = #{i}, #{sw} ======"

      if a.swap(i, sw) && a.sorted?
        puts ">> ARRAY: IS SORTED. NOW!"
        return true
      end
      a.swap(i, sw)
    end
  end

  # 3 . Else... > FLASE
  puts ">> ARRAY: CAN'T BE SORTED BY ONE SWAP!!!"
  return false
end

sortable_by_one?(A)

I found a simpler way. Check my gist again.