Given two singly linked lists that intersect at some point, find the intersecting node. Do this in O(M + N) time (where M and N are the lengths of the lists) and constant space. For example, given A = 3 -> 7 -> 8 -> 10 -> 1 and B = 99 -> 1 -> 8 -> 10, return the node with value 8.
Example:
>>> class LinkedListNode(object):
...
... def __init__(self, value, child=None):
... self.value = value
... self.next = child
...
... def add(self, value):
... return LinkedListNode(value, self)
...
... @classmethod
... def len(cls, node):
... count = 0
... while node:
... node = node.next
... count += 1
... return count
>>> common_tail = LinkedListNode(1).add(10).add(8)
>>> list_a = LinkedListNode(7, common_tail).add(3)
>>> list_b = LinkedListNode(1, common_tail).add(99).add(14)
>>> coding_problem_20(list_a, list_b)
8