MinMaxDivision solution https://codility.com/programmers/lessons/14-binary_search_algorithm/min_max_division/start/

min_max_division.rb

# Returns whether a can be split in max_blocks with a
# max sum equal or lower to max_sum
def can_split_in_blocks?(a, max_sum, max_blocks)
  n_blocks = 0
  current_block_sum = 0

  a.each_with_index do |elm, i|
    if current_block_sum + elm <= max_sum && i > 0
      # Use the current block
      current_block_sum += elm
    else
      # Start a new block
      n_blocks += 1
      current_block_sum = elm
    end
  end

  n_blocks <= max_blocks
end

def solution(k, m, a)
  result_lower_bound = a.max
  result_upper_bound = a.inject(&:+)

  return result_upper_bound if k == 1
  return result_lower_bound if k >= a.size

  candidates = (result_lower_bound..result_upper_bound).to_a

  result = candidates.bsearch do |c|
    can_split_in_blocks?(a, c, k)
  end

  result
end


require 'minitest/autorun'

class Tests < MiniTest::Unit::TestCase
  def test_can_split_in_blocks
    assert_equal true, can_split_in_blocks?([2, 1, 5, 1, 2, 2, 2], 6, 3)
  end

  def test_can_not_split_in_blocks
    assert_equal false, can_split_in_blocks?([2, 1, 5, 1, 2, 2, 2], 5, 3)
  end

  def test_example_input
    assert_equal 6, solution(3, 5, [2, 1, 5, 1, 2, 2, 2])
  end
end