Linked List Cycle

01 · Question

Given head, determine if the linked list has a cycle in it.

Use fast and slow pointers (Floyd's cycle detection).

02 · Solution

Reference solution

1def hasCycle(head: Optional[ListNode]) -> bool:
2    slow = head
3    fast = head
4    
5    while fast and fast.next:
6        slow = slow.next
7        fast = fast.next.next
8        if slow == fast:
9            return True
10    
11    return False

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