LC 0142 [M] Linked List Cycle II - ALawliet/algorithms GitHub Wiki
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def detectCycle(self, head: Optional[ListNode]) -> Optional[ListNode]:
fast = slow = head
while fast and fast.next:
fast = fast.next.next
slow = slow.next
if fast == slow:
break # there must be a cycle and slow and fast are on the cycle
else: # got to the end without breaking
return None # if not (fast and fast.next): return None
while head != fast:
head = head.next
fast = fast.next
return head