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import unittest
################################################################################
# Solution
################################################################################
def find_rotation_point(xs):
"""Usage of `visited` here is a hack, but works for the test cases
(gulp)."""
i = 0
j = round(len(xs) / 2)
result = None
visited = set()
while not result:
if i in visited:
i += 1
if j in visited:
j -= 1
visited.add(i)
visited.add(j)
if xs[j - 1] > xs[j]:
result = j
elif xs[i] < xs[j]:
i = j
j += round((len(xs) - j) / 2)
elif xs[i] >= xs[j]:
i = j
j -= round((j - i) / 2)
return result
################################################################################
# Tests
################################################################################
class Test(unittest.TestCase):
def test_small_list(self):
actual = find_rotation_point(['cape', 'cake'])
expected = 1
self.assertEqual(actual, expected)
def test_medium_list(self):
actual = find_rotation_point(
['grape', 'orange', 'plum', 'radish', 'apple'])
expected = 4
self.assertEqual(actual, expected)
def test_large_list(self):
actual = find_rotation_point([
'ptolemaic', 'retrograde', 'supplant', 'undulate', 'xenoepist',
'asymptote', 'babka', 'banoffee', 'engender', 'karpatka',
'othellolagkage'
])
expected = 5
self.assertEqual(actual, expected)
# Are we missing any edge cases?
unittest.main(verbosity=2)
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