89 lines
2.6 KiB
Python
89 lines
2.6 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 contains_cycle(x):
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if not x:
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return False
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elif not x.next:
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return False
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a = x
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b = x.next
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while b.next:
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if a == b:
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return True
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a = a.next
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b = b.next.next
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return False
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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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class LinkedListNode(object):
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def __init__(self, value, next=None):
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self.value = value
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self.next = next
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def test_linked_list_with_no_cycle(self):
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fourth = Test.LinkedListNode(4)
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third = Test.LinkedListNode(3, fourth)
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second = Test.LinkedListNode(2, third)
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first = Test.LinkedListNode(1, second)
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result = contains_cycle(first)
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self.assertFalse(result)
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def test_cycle_loops_to_beginning(self):
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fourth = Test.LinkedListNode(4)
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third = Test.LinkedListNode(3, fourth)
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second = Test.LinkedListNode(2, third)
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first = Test.LinkedListNode(1, second)
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fourth.next = first
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result = contains_cycle(first)
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self.assertTrue(result)
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def test_cycle_loops_to_middle(self):
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fifth = Test.LinkedListNode(5)
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fourth = Test.LinkedListNode(4, fifth)
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third = Test.LinkedListNode(3, fourth)
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second = Test.LinkedListNode(2, third)
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first = Test.LinkedListNode(1, second)
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fifth.next = third
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result = contains_cycle(first)
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self.assertTrue(result)
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def test_two_node_cycle_at_end(self):
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fifth = Test.LinkedListNode(5)
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fourth = Test.LinkedListNode(4, fifth)
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third = Test.LinkedListNode(3, fourth)
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second = Test.LinkedListNode(2, third)
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first = Test.LinkedListNode(1, second)
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fifth.next = fourth
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result = contains_cycle(first)
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self.assertTrue(result)
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def test_empty_list(self):
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result = contains_cycle(None)
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self.assertFalse(result)
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def test_one_element_linked_list_no_cycle(self):
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first = Test.LinkedListNode(1)
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result = contains_cycle(first)
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self.assertFalse(result)
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def test_one_element_linked_list_cycle(self):
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first = Test.LinkedListNode(1)
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first.next = first
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result = contains_cycle(first)
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self.assertTrue(result)
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unittest.main(verbosity=2)
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