This notebook was prepared by Donne Martin. Source and license info is on GitHub.
Complexity:
%run ../linked_list/linked_list.py
class MyLinkedList(LinkedList):
def kth_to_last_elem(self, k):
if self.head is None:
return None
fast = self.head
slow = self.head
# Give fast a headstart, incrementing it
# once for k = 1, twice for k = 2, etc
for _ in range(k):
fast = fast.next
# If k >= num elements, return None
if fast is None:
return None
# Increment both pointers until fast reaches the end
while fast.next is not None:
fast = fast.next
slow = slow.next
return slow.data
%%writefile test_kth_to_last_elem.py
import unittest
class Test(unittest.TestCase):
def test_kth_to_last_elem(self):
print('Test: Empty list')
linked_list = MyLinkedList(None)
self.assertEqual(linked_list.kth_to_last_elem(0), None)
print('Test: k >= len(list)')
self.assertEqual(linked_list.kth_to_last_elem(100), None)
print('Test: One element, k = 0')
head = Node(2)
linked_list = MyLinkedList(head)
self.assertEqual(linked_list.kth_to_last_elem(0), 2)
print('Test: General case')
linked_list.insert_to_front(1)
linked_list.insert_to_front(3)
linked_list.insert_to_front(5)
linked_list.insert_to_front(7)
self.assertEqual(linked_list.kth_to_last_elem(2), 3)
print('Success: test_kth_to_last_elem')
def main():
test = Test()
test.test_kth_to_last_elem()
if __name__ == '__main__':
main()
Overwriting test_kth_to_last_elem.py
%run -i test_kth_to_last_elem.py
Test: Empty list Test: k >= len(list) Test: One element, k = 0 Test: General case Success: test_kth_to_last_elem