chop.rb

def chop(search_for, sorted_list)
  if sorted_list[0] == search_for
    return 0
  elsif sorted_list.size == 1 || sorted_list.empty?
    return -1
  elsif sorted_list[0] > search_for
    return -1
  else
    halfway = sorted_list.size / 2
    first_half = sorted_list[0,halfway]
    second_half = sorted_list[halfway,halfway + 1]
    if second_half[0] > search_for
      return chop(search_for, first_half)
    else
      return chop(search_for, second_half)
    end
  end 
end

Test Results

Loaded suite test_chop
Started
.
Finished in 0.002076 seconds.

1 tests, 19 assertions, 0 failures, 0 errors

test_chop.rb

require 'chop'
require 'test/unit'

class TestChop < Test::Unit::TestCase

  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(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