This notebook was prepared by Donne Martin. Source and license info is on GitHub.

# Challenge Notebook¶

## Constraints¶

• Is this a singly linked list?
• Yes
• Can we assume we are always passed a circular linked list?
• No
• When we find a loop, do we return the node or the node's data?
• The node
• Can we assume we already have a linked list class that can be used for this problem?
• Yes

## Test Cases¶

• Empty list -> None
• Not a circular linked list -> None
• One element
• Two or more elements
• Circular linked list general case

## Algorithm¶

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

## Code¶

In [ ]:
%run ../linked_list/linked_list.py

In [ ]:
class MyLinkedList(LinkedList):

def find_loop_start(self):
# TODO: Implement me
pass


## Unit Test¶

The following unit test is expected to fail until you solve the challenge.

In [ ]:
# %load test_find_loop_start.py
import unittest

class TestFindLoopStart(unittest.TestCase):

def test_find_loop_start(self):
print('Test: Empty list')

print('Test: Not a circular linked list: One element')

print('Test: Not a circular linked list: Two elements')

print('Test: Not a circular linked list: Three or more elements')

print('Test: General case: Circular linked list')
node10 = Node(10)
node9 = Node(9, node10)
node8 = Node(8, node9)
node7 = Node(7, node8)
node6 = Node(6, node7)
node5 = Node(5, node6)
node4 = Node(4, node5)
node3 = Node(3, node4)
node2 = Node(2, node3)
node1 = Node(1, node2)
node0 = Node(0, node1)
node10.next = node3

print('Success: test_find_loop_start')

def main():
test = TestFindLoopStart()
test.test_find_loop_start()

if __name__ == '__main__':
main()


## Solution Notebook¶

Review the Solution Notebook for a discussion on algorithms and code solutions.