"""
 chop() binary search from
 http://codekata.pragprog.com/2007/01/kata_two_karate.html

 Programming Workshop | April 3
"""

def chop(n, list):
    """ Return index of where n is in list,
        -1 if not found. """
    if len(list) == 0:
        return -1
    if len(list) == 1:
        if list[0] == n:
            return 0
        else:
            return -1
    split_index = len(list)/2
    answer1 = chop(n, list[:split_index])
    if answer1 != -1:
        return answer1
    answer2 = chop(n, list[split_index:])
    if answer2 != -1:
        return answer2 + split_index
    return -1

def assert_equal(a, b):
    assert a == b, "failed 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(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]))
    print "Passed all tests."

test_chop()