de039c7133
Solves an InterviewCake.com problem that returns the index of the element in a list that should be the first element in that list. It's an exercise that's useful for seeing other applications of a binary search.
55 lines
1.2 KiB
Python
55 lines
1.2 KiB
Python
import unittest
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from math import floor
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def midpoint(a, b):
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return a + floor((b - a) / 2)
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def do_find_rotation_point(a, b, xs):
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i = midpoint(a, b)
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count = b - a + 1
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if count == 2:
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if xs[a] > xs[b]:
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return b
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else:
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return -1
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if i in {a, b}:
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return i
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if xs[a] < xs[i]:
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return do_find_rotation_point(i, b, xs)
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else:
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return do_find_rotation_point(a, i, xs)
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def find_rotation_point(xs):
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return do_find_rotation_point(0, len(xs) - 1, xs)
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# Tests
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class Test(unittest.TestCase):
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def test_small_list(self):
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actual = find_rotation_point(['cape', 'cake'])
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expected = 1
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self.assertEqual(actual, expected)
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def test_medium_list(self):
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actual = find_rotation_point(
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['grape', 'orange', 'plum', 'radish', 'apple'])
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expected = 4
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self.assertEqual(actual, expected)
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def test_large_list(self):
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actual = find_rotation_point([
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'ptolemaic', 'retrograde', 'supplant', 'undulate', 'xenoepist',
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'asymptote', 'babka', 'banoffee', 'engender', 'karpatka',
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'othellolagkage'
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])
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expected = 5
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self.assertEqual(actual, expected)
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unittest.main(verbosity=2)
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