divide_and_conquer.rb

# The MIT License
# 
# All contents Copyright (c) 2004-2008 Reginald Braithwaite
# <http://braythwayt.com>  except as otherwise noted.
# 
# 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
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
# 
# http://www.opensource.org/licenses/mit-license.php

public

def sum_squares_3(list)
  divide_and_conquer(
    list,
    :divisible? => lambda { |value| value.kind_of?(Enumerable) },
    :conquer    => lambda { |value| value ** 2 },
    :divide     => lambda { |value| value },
    :recombine  => lambda { |list| list.inject() { |x,y| x + y } }
  )
end

def rotate_3(square)
  divide_and_conquer(
    square,
    :divisible? => lambda { |value| value.kind_of?(Enumerable) && value.size > 1 },
    :conquer => lambda { |value| value },
    :divide => lambda do |square|
  	  half_sz = square.size / 2
  	  sub_square = lambda do |row, col|
  	    square.slice(row, half_sz).map { |a_row| a_row.slice(col, half_sz) }
  	  end
  	  upper_left = sub_square.call(0,0)
  	  lower_left = sub_square.call(half_sz,0)
  	  upper_right = sub_square.call(0,half_sz)
  	  lower_right = sub_square.call(half_sz,half_sz)
  	  [upper_left, lower_left, upper_right, lower_right]
    end,
    :recombine => lambda do |list|
  	  upper_left, lower_left, upper_right, lower_right = list
  	  upper_right.zip(lower_right).map { |l,r| l + r } +
  	  upper_left.zip(lower_left).map { |l,r| l + r }
    end
  )
end

private

def divide_and_conquer(value, steps)
  if steps[:divisible?].call(value)
    steps[:recombine].call(
      steps[:divide].call(value).map { |sub_value| divide_and_conquer(sub_value, steps) }
    )
  else
    steps[:conquer].call(value)
  end
end

p sum_squares_3([1, 2, 3, [[4,5], 6], [[[7]]]])

p rotate_3([[1,2,3,4], [5,6,7,8], [9,10,11,12], [13,14,15,16]])