merge_sort.rb

#!/usr/bin/ruby

# Copyright (c) 2012 clowwindy
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

def merge (left, right, comparison)
  result = []
  while (left.length > 0) and (right.length > 0)
    if comparison.call(left[0], right[0]) <= 0
      result.push left.shift()
    else
      result.push right.shift()
    end
  end
  result.push left.shift() while left.length > 0
  result.push right.shift() while right.length > 0
  result
end

def merge_sort (array, comparison)
  return array if array.size < 2
  middle = (array.size / 2).ceil
  merge(merge_sort(array.slice(0, middle), comparison), merge_sort(array.slice(middle .. array.size), comparison), comparison)
end