leetcode

Leetcode submissions
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linked-list-cycleV2.py (715B)

      1 # Definition for singly-linked list.
      2 # class ListNode:
      3 #     def __init__(self, x):
      4 #         self.val = x
      5 #         self.next = None
      6 
      7 
      8 class Solution:
      9     def hasCycle(self, head: Optional[ListNode]) -> bool:
     10 
     11         # two pointers, one fast, one slow
     12         # if fast catches slow, issue
     13         # if fast reaches end, success
     14 
     15         if head is None:
     16             return False
     17 
     18         fast_ptr = head.next
     19         slow_ptr = head
     20 
     21         while fast_ptr is not None:
     22             if fast_ptr == slow_ptr:
     23                 return True
     24 
     25             fast_ptr = fast_ptr.next
     26 
     27             if fast_ptr is not None:
     28                 fast_ptr = fast_ptr.next
     29 
     30             slow_ptr = slow_ptr.next
     31 
     32         return False