quick_sort.rb

class Array
  def selection_sort
    (0...length).each do |i|
      min = i
      
      (i+1...length).each do |j|
        min = j if self[j] < self[i]
      end
      self[i], self[min] = self[min], self[i]
    end
  end
  
  def insertion_sort
    (1...length).each do |i|
      j = i-1
      while (self[i] < self[j] && j >= 0)
        self[i], self[j] = self[j], self[i]
        j -= 1
        i -= 1
      end
    end
  end
  
  def quick_sort
    return self if length <= 1
    pivot = self[length/2]
    find_all {|x| x < pivot }.quick_sort +
    find_all {|x| x == pivot} +
    find_all {|x| x > pivot}.quick_sort
  end
end