my-snail-sort.rb

require 'minitest/autorun'

SortSnail = -> (elements, result = []) {
  return result if elements.empty?

  bottom_limit = 0
  top_limit = elements.count - 1

  loop do
    result.concat elements[bottom_limit][bottom_limit..top_limit]

    (bottom_limit + 1..top_limit).each do |row|
      result << elements[row][top_limit]
    end

    result.concat elements[top_limit][bottom_limit...top_limit].reverse

    (top_limit - 1).downto(bottom_limit + 1).each do |row|
      result << elements[row][bottom_limit]
    end

    bottom_limit += 1
    top_limit -= 1

    break if bottom_limit > top_limit
  end

  result
}

describe SortSnail do
  it 'should handle empty arrays' do
    elements = []
    SortSnail.(elements).must_equal []
  end

  it 'should handle pair arrays' do
    elements = [
      [ 1, 2 ],
      [ 4, 9 ],
    ]
    SortSnail.(elements).must_equal [
      1, 2, 9, 4
    ]
  end

  it 'should handle odd arrays' do
    elements = [
      [ 1, 2, 3],
      [ 4, 5, 6],
      [ 7, 8, 9],
    ]
    SortSnail.(elements).must_equal [
      1, 2, 3, 6, 9, 8, 7, 4, 5
    ]
  end

  it 'should handle big arrays' do
    elements = [
      [ 1,  2,  3,  4,  5,  6],
      [ 7,  8,  9,  10, 11, 12],
      [ 13, 14, 15, 16, 17, 19],
      [ 20, 21, 22, 23, 24, 25],
      [ 26, 27, 28, 29, 30, 31],
      [ 32, 33, 34, 35, 36, 37],
    ]
    SortSnail.(elements).must_equal [
      1, 2, 3, 4, 5, 6, 12, 19, 25, 31, 37, 36, 35, 34, 33, 32,
      26, 20, 13, 7, 8, 9, 10, 11, 17, 24, 30, 29, 28, 27, 21, 14,
      15, 16, 23, 22
    ]
  end

end


require 'ruby-prof'
elements = Array.new(500) {Array.new(500) { rand 20 }}
RubyProf.start
SortSnail.(elements)
result = RubyProf.stop
printer = RubyProf::FlatPrinter.new result
printer.print STDOUT

my-snail-sort.rb output

➜  katas  ruby my-snail-sort.rb
Thread ID: 70156823111380
Fiber ID: 70156822837020
Total: 0.096955
Sort by: self_time

 %self      total      self      wait     child     calls  name
 50.11      0.049     0.049     0.000     0.000      500   Integer#downto
 44.50      0.043     0.043     0.000     0.000      250   Range#each
  2.84      0.097     0.003     0.000     0.094        1   Kernel#loop
  1.14      0.001     0.001     0.000     0.000      500   Array#concat
  0.51      0.000     0.000     0.000     0.000      250   Array#reverse
  0.50      0.000     0.000     0.000     0.000      500   Array#[]
  0.35      0.044     0.000     0.000     0.043      250   Enumerator#each
  0.04      0.097     0.000     0.000     0.097        1   Global#[No method]
  0.01      0.097     0.000     0.000     0.097        1   Proc#call
  0.00      0.000     0.000     0.000     0.000        1   Array#count

* indicates recursively called methods
Run options: --seed 59476

# Running tests:

....

Finished tests in 0.000605s, 6611.5702 tests/s, 6611.5702 assertions/s.

4 tests, 4 assertions, 0 failures, 0 errors, 0 skips

smaller-snail-sort.rb

require 'minitest/autorun'

SortSnail = -> (array) {
  array.empty? ? [] : array.shift + SortSnail.(array.transpose.reverse)
}

describe SortSnail do
  it 'should handle empty arrays' do
    elements = []
    SortSnail.(elements).must_equal []
  end

  it 'should handle pair arrays' do
    elements = [
      [ 1, 2 ],
      [ 4, 9 ],
    ]
    SortSnail.(elements).must_equal [
      1, 2, 9, 4
    ]
  end

  it 'should handle odd arrays' do
    elements = [
      [ 1, 2, 3],
      [ 4, 5, 6],
      [ 7, 8, 9],
    ]
    SortSnail.(elements).must_equal [
      1, 2, 3, 6, 9, 8, 7, 4, 5
    ]
  end

  it 'should handle big arrays' do
    elements = [
      [ 1,  2,  3,  4,  5,  6],
      [ 7,  8,  9,  10, 11, 12],
      [ 13, 14, 15, 16, 17, 19],
      [ 20, 21, 22, 23, 24, 25],
      [ 26, 27, 28, 29, 30, 31],
      [ 32, 33, 34, 35, 36, 37],
    ]
    SortSnail.(elements).must_equal [
      1, 2, 3, 4, 5, 6, 12, 19, 25, 31, 37, 36, 35, 34, 33, 32,
      26, 20, 13, 7, 8, 9, 10, 11, 17, 24, 30, 29, 28, 27, 21, 14,
      15, 16, 23, 22
    ]
  end

end


require 'ruby-prof'
elements = Array.new(500) {Array.new(500) { rand 20 }}
RubyProf.start
SortSnail.(elements)
result = RubyProf.stop
printer = RubyProf::FlatPrinter.new result
printer.print STDOUT

smaller-snail-sort.rb output

➜  katas  ruby smaller-snail-sort.rb
Thread ID: 70117983856340
Fiber ID: 70117983582840
Total: 24.090672
Sort by: self_time

 %self      total      self      wait     child     calls  name
 49.27     11.869    11.869     0.000     0.000      999   Array#transpose
  0.03      0.007     0.007     0.000     0.000      999   Array#reverse
  0.01      0.002     0.002     0.000     0.000      999   Array#shift
  0.00     24.091     0.001     0.000    24.090     1000  *Proc#call
  0.00     24.091     0.000     0.000    24.091        1   Global#[No method]

* indicates recursively called methods
Run options: --seed 38546

# Running tests:

....

Finished tests in 0.000584s, 6849.3151 tests/s, 6849.3151 assertions/s.

4 tests, 4 assertions, 0 failures, 0 errors, 0 skips