1. Solution to http://codekata.com/kata/kata02-karate-chop/

karate_chop.rb

require "pry"

def chop number, numbers, acc = 0
  return -1 if numbers.nil? || numbers.empty?

  pivot_pos = (numbers.size / 2)
  pivot = numbers[pivot_pos]
  return pivot_pos + acc if pivot == number

  smaller = numbers.slice(0, pivot_pos)
  res = chop(number, smaller, acc)
  return res if res != -1

  bigger = numbers.slice(pivot_pos, numbers.size-1)
  chop(number, bigger, acc + pivot_pos)
end

require "minitest/autorun"

class Test < Minitest::Test

  def test_chop
    assert_equal(-1, chop(3, []))
    assert_equal(-1, chop(3, [1]))
    assert_equal(0,  chop(1, [1]))
    ##
    assert_equal(0,  chop(1, [1, 3, 5]))
    assert_equal(1,  chop(3, [1, 3, 5]))
    assert_equal(1,  chop(5, [3, 5]))
    assert_equal(2,  chop(5, [1, 3, 5]))
    assert_equal(-1, chop(0, [1, 3, 5]))
    assert_equal(-1, chop(2, [1, 3, 5]))
    assert_equal(-1, chop(4, [1, 3, 5]))
    assert_equal(-1, chop(6, [1, 3, 5]))
    ##
    assert_equal(0,  chop(1, [1, 3, 5, 7]))
    assert_equal(1,  chop(3, [1, 3, 5, 7]))
    assert_equal(2,  chop(5, [1, 3, 5, 7]))
    assert_equal(3,  chop(7, [1, 3, 5, 7]))
    assert_equal(-1, chop(0, [1, 3, 5, 7]))
    assert_equal(-1, chop(2, [1, 3, 5, 7]))
    assert_equal(-1, chop(4, [1, 3, 5, 7]))
    assert_equal(-1, chop(6, [1, 3, 5, 7]))
    assert_equal(-1, chop(8, [1, 3, 5, 7]))
  end

end