57 lines
1.6 KiB
Python
57 lines
1.6 KiB
Python
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import unittest
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################################################################################
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# Solution
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################################################################################
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def find_duplicate(xs):
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self_ref_count = 0
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for i in range(len(xs)):
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if xs[i] == i + 1:
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self_ref_count += 1
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hops = len(xs) - 1 - self_ref_count
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current = xs[-1]
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while hops > 0:
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current = xs[current - 1]
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hops -= 1
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return current
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################################################################################
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# Tests
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################################################################################
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class Test(unittest.TestCase):
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# TODO: Debug why this fails.
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def test_darren_from_interview_cake(self):
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actual = find_duplicate([4, 1, 8, 3, 2, 7, 6, 5, 4])
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expected = 4
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self.assertEqual(actual, expected)
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def test_just_the_repeated_number(self):
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actual = find_duplicate([1, 1])
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expected = 1
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self.assertEqual(actual, expected)
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def test_short_list(self):
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actual = find_duplicate([1, 2, 3, 2])
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expected = 2
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self.assertEqual(actual, expected)
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def test_last_cycle(self):
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actual = find_duplicate([3, 4, 2, 3, 1, 5])
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expected = 3
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self.assertEqual(actual, expected)
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def test_medium_list(self):
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actual = find_duplicate([1, 2, 5, 5, 5, 5])
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expected = 5
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self.assertEqual(actual, expected)
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def test_long_list(self):
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actual = find_duplicate([4, 1, 4, 8, 3, 2, 7, 6, 5])
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expected = 4
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self.assertEqual(actual, expected)
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unittest.main(verbosity=2)
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