Various sort algorithms in Ruby

sort.rb

# Plain bubble sort.
def bubble_sort(array)
  loop do
    swapped = false
    (array.size - 1).times do |i|
      if array[i] > array[i+1]
        array[i], array[i+1] = array[i+1], array[i]
        swapped = true
      end
    end
    break unless swapped
  end
  array
end

array = Array.new(10) { rand(10) }
puts array.inspect
puts ">>>" + bubble_sort(array).inspect

# Bubble sort with lambda.
def bubble_sort(array)
  swap = lambda { |arr, i, j| arr[i], arr[j] = arr[j], arr[i] if arr[i] > arr[j] }
  loop do
    swapped = false
    (array.size - 1).times do |i|
      swapped ||= swap[array, i, i+1]
    end
    break unless swapped
  end
  array
end

array = Array.new(10) { rand(10) }
puts array.inspect
puts ">>>" + bubble_sort(array).inspect

# Selection sort.
def selection_sort(array)
  (array.size).times do |i|
    index = array[i .. -1].each_with_index.min[1]
    array[i], array[index+i] = array[index+i], array[i] if array[index+i] < array[i]
  end
  array
end

array = Array.new(20) { rand(20) }
puts array.inspect
puts ">>>" + selection_sort(array).inspect


# Merge sort.
def merge_sort(array)
  return array if array.size < 2
  middle = array.size / 2
  head = merge_sort(array[0, middle])
  tail = merge_sort(array.drop(middle))

  # merged = []
  # until head.empty? or tail.empty?
  #   merged << (head.first <= tail.first ? head.shift : tail.shift)
  # end
  # merged + head + tail
  # 
  Array.new(head.size + tail.size) do |i|
    if head.empty? || tail.empty?
      head.shift || tail.shift
    else
      head[0] <= tail[0] ? head.shift : tail.shift
    end
  end
end

array = Array.new(20) { rand(20) }
puts array.inspect
puts ">>>" + merge_sort(array).inspect

# Quick sort.
def quick_sort(array)
  return [] if array.empty?
  pivot = array.shift
  quick_sort(array.select{ |i| i <= pivot }) + [ pivot ] + quick_sort(array.select{ |i| i > pivot })
end

array = Array.new(21) { rand(21) }
puts array.inspect
puts ">>>" + quick_sort(array).inspect